Methods of Manufacturing Electronic Display Devices Employing Nozzle-Droplet Combination Techniques to Deposit Fluids in Substrate Locations within Precise Tolerances

ABSTRACT

An ink printing process employs per-nozzle droplet volume measurement and processing software that plans droplet combinations to reach specific aggregate ink fills per target region, guaranteeing compliance with minimum and maximum ink fills set by specification. In various embodiments, different droplet combinations are produced through different print head/substrate scan offsets, offsets between print heads, the use of different nozzle drive waveforms, and/or other techniques. Optionally, patterns of fill variation can be introduced so as to mitigate observable line effects in a finished display device. The disclosed techniques have many other possible applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Utility patent applicationSer. No. 14/162,525, filed Jan. 23, 2014 for “Techniques For Print InkVolume Control To Deposit Fluids Within Precise Tolerances,” filed onbehalf of first named inventor Conor Francis Madigan.

U.S. Utility application Ser. No. 14/162,525 is, in turn, a continuationof PCT Patent Application No. PCT/US13/77720, filed Dec. 24, 2013, whichclaims priority to U.S. Provisional Patent Application No. 61/746,545,filed Dec. 27, 2012 for “Smart Mixing,” filed on behalf of first namedinventor Conor Francis Madigan. U.S. Utility application Ser. No.14/162,525 also claims priority to each of the following applications:U.S. Provisional Patent Application No. 61/822,855 for “Systems andMethods Providing Uniform Printing of OLED Panels,” filed on behalf offirst named inventor Nahid Harjee on May 13, 2013; U.S. ProvisionalPatent Application No. 61/842,351 for “Systems and Methods ProvidingUniform Printing of OLED Panels,” filed on behalf of first namedinventor Nahid Harjee on Jul. 2, 2013; U.S. Provisional PatentApplication No. 61/857,298 for “Systems and Methods Providing UniformPrinting of OLED Panels,” filed on behalf of first named inventor NahidHarjee on Jul. 23, 2013; U.S. Provisional Patent Application No.61/898,769 for “Systems and Methods Providing Uniform Printing of OLEDPanels,” filed on behalf of first named inventor Nahid Harjee on Nov. 1,2013; U.S. Provisional Patent Application No. 61/920,715 for “Techniquesfor Print Ink Volume Control To Deposit Fluids Within PreciseTolerances,” filed on behalf of first named inventor Nahid Harjee onDec. 24, 2013; and Taiwan Patent Application No. 102148330 for“Techniques for Print Ink Volume Control To Deposit Fluids WithinPrecise Tolerances,” filed on behalf of first named inventor NahidHarjee on Dec. 26, 2013. Each of the aforementioned patent applicationsis hereby incorporated by reference.

This disclosure relates to use of a printing process to transfer a fluidto target regions of a substrate. In one non-limiting application,techniques provided by this disclosure can be applied to a manufacturingprocess for large scale displays.

BACKGROUND

In a printing process where a print head has multiple nozzles, not everynozzle reacts to a standard drive waveform the same way, i.e., eachnozzle can produce a droplet of slightly different volume. In situationswhere the nozzles are relied upon to deposit fluid droplets intorespective fluid deposition areas (“target regions”), lack ofconsistency can lead to problems.

FIG. 1A is used to introduce this nozzle-droplet inconsistency issue,with an illustrative diagram generally referenced using numeral 101. InFIG. 1, a print head 103 is seen to have five ink nozzles, which areeach depicted using small triangles at the bottom of the print head,each respectively numbered (1)-(5). It should be assumed that in anexample application, it is desired to deposit fifty picoliters (50.00pL) of a fluid into each of five specific target regions of an array ofsuch regions, and further, that each of five nozzles of a print head isto eject ten picoliters (10.00 pl) of fluid with each relative movement(“pass” or “scan”) between the print head and a substrate into each ofthe various target regions. The target regions can be any surface areasof the substrate, including adjoining unseparated areas (e.g., such thatdeposited fluid ink partially spreads to blend together betweenregions), or respective, fluidically-isolated regions. These regions aregenerally represented in FIG. 1 using ovals 104-108, respectively. Thus,it might be assumed that exactly five passes of the print head arenecessary as depicted to fill each of the five specific target regions.However, print head nozzles will in practice have some minor variationsin structure or actuation, such that a given drive waveform applied torespective nozzle transducers yields slightly different droplet volumesfor each nozzle. As depicted in FIG. 1A, for example, the firing ofnozzle (1) yields a droplet volume of 9.80 picoliters (pL) with eachpass, with five 9.80 pL droplets being depicted within oval 104. Notethat each of the droplets is represented in the figure by a distinctlocation within the target region 104, but in practice, the location ofeach of the droplets may be the same or may overlap. Nozzles (2)-(5), bycontrast, yield slightly different, respective droplet volumes of 10.01pL, 9.89 pL, 9.96 pL and 10.03 pL. With five passes between print headand substrate where each nozzle deposits fluid on a mutually-exclusivebasis into the target regions 104-108, this deposition would result in atotal deposited ink volume variation of 1.15 pL across the five targetregions; this can be unacceptable for many applications. For example, insome applications, discrepancy of as little as one percent (or even muchless) in deposited fluid can cause issues.

One example application where this issue arises is in a manufacturingprocess applied to the fabrication of displays, such as organiclight-emitting diode (“OLED”) displays. Where a printing process is usedto deposit an ink carrying light-generating materials of such displays,the volume discrepancy across rows or columns of fluid receptacles or“wells” (e.g., with 3 such receptacles per pixel) can lead to visiblecolor or lighting defects in a displayed image. Note that “ink” as usedherein refers to any fluid applied to a substrate by nozzles of a printhead irrespective of color characteristics; in thementioned-manufacturing application, ink is typically deposited in placeand then processed or cured in order to directly form a permanentmaterial layer. Television and display manufacturers will thereforeeffectively specify precise volume ranges that must be observed with ahigh-degree of precision, e.g., 50.00 pL, ±0.25 pL in order for aresultant product to be considered acceptable; note that in thisapplication, the specified tolerance must be within one-half percent ofthe target of 50.00 pL. In an application where each nozzle representedby FIG. 1 was to deposit into pixels in respective horizontal lines of ahigh-definition television (“HDTV”) screen, the depicted variation of49.02 pL-50.17 pL might therefore yield unacceptable quantity. Whiledisplay technologies have been cited as an example, it should beunderstood that the nozzle-droplet inconsistency problem can arise inother contexts.

In FIG. 1A, nozzles are specifically aligned with target regions (e.g.,wells) such that specific nozzles print into specific target regions. InFIG. 1B, an alternate case 151 is shown in which the nozzles are notspecially aligned, but in which nozzle density is high relative totarget region density; in such a case, whichever nozzles happen totraverse specific target regions during a scan or pass are used to printinto those target regions, with potentially several nozzles traversingeach target region in each pass. In the example shown, the print head153 is seen to have five ink nozzles and the substrate is seen to havetwo target regions 154-155, each located such that nozzles (1) and (2)will traverse target region 154, nozzles (4) and (5) will traversetarget region 155, and nozzle (3) will not traverse either targetregion. As shown, in each pass, one or two droplets are deposited intoeach well, as depicted. Note that once again, the droplets can bedeposited in a manner that is overlapping or at discrete points withineach target region, and that the particular illustration in FIG. 1B isillustrative only; as with the example presented in FIG. 1A, it is onceagain assumed that it is desired to deposit fifty picoliters (50.00 pL)of a fluid into each of target regions 154-155, and that each nozzle hasa nominal droplet volume of approximately 10.00 pL. Utilizing the sameper nozzle droplet volume variation as observed in connection with theexample of FIG. 1A, and assuming that each nozzle that overlaps with atarget region on a given pass will deliver a droplet into that targetregion up until a total of five droplets have been delivered, it isobserved that the target regions are filled in three passes and there isa total deposited ink volume variation from the target of 50.00 pL of0.58 pL across the two target regions; this, again, can be unacceptablefor many applications.

While techniques have been proposed to address the consistency problem,generally speaking, these techniques either still do not reliablyprovide fill volumes that stay within the desired tolerance range orthey dramatically increase manufacturing time and cost, i.e., they areinconsistent with a goal of having high quality with a low consumerprice-point; such quality and low price-point can be key forapplications where commodity products, such as HDTVs, are concerned.

What is therefore needed are techniques useful in depositing fluid intotarget regions of a substrate using a print head with nozzles. Morespecifically, what is needed are techniques for precisely controllingdeposited fluid volumes in respective target regions of a substrategiven variations in nozzle-droplet ejection volumes, ideally on acost-effective basis that permits fast fluid deposition operations andthus improves the speed of device fabrication. The techniques describedbelow satisfy these needs and provide further, related advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram that presents a hypothetical problem of depositingink in target regions of a substrate where a print head with fivenozzles is used to deposit a target fill of 50.00 pL in each of fivespecific target regions.

FIG. 1B is another diagram that presents a hypothetical problem ofdepositing ink in target regions of a substrate where a print head withfive nozzles is used to deposit a target fill of 50.00 pL in each of twospecific target regions.

FIG. 2A is an illustrative diagram showing a hypothetical arrangement ofa printer and substrate, in an application where the substrate isultimately to form a display panel having pixels.

FIG. 2B is a cross-sectional close-up view of the print head andsubstrate of FIG. 2A, taken from the perspective of lines A-A from FIG.2A.

FIG. 3A is a diagram similar to FIG. 1A, but illustrates the use ofcombinations of droplet volumes to reliably produce ink fill volumes foreach target region within a predetermined tolerance range; in oneoptional embodiment, different droplet volume combinations are producedfrom a set of predetermined nozzle firing waveforms, and in anotheroptional embodiment, different droplet volume combinations are producedfrom respective nozzles of the print head using relative motion (305)between print head and substrate.

FIG. 3B is a diagram used to illustrate relative print head/substratemotion and the ejection of different droplet volume combinations intorespective target regions of a substrate.

FIG. 3C is a diagram similar to FIG. 1B, but illustrates the use ofcombinations of droplet volumes to reliably produce ink fill volumes foreach target region within a predetermined tolerance range; in oneoptional embodiment, different droplet volume combinations are producedfrom a set of predetermined nozzle firing waveforms, and in anotheroptional embodiment, different droplet volume combinations are producedfrom respective nozzles of the print head using relative motion (372)between print head and substrate.

FIG. 4 provides an illustrative view showing a series of optional tiers,products or services that can each independently embody the techniquesintroduced earlier.

FIG. 5 provides a block diagram showing a method of planningcombinations of droplets for each target region of a substrate; thismethod can be applied to either optional embodiment introduced by FIG.3A.

FIG. 6A provides a block diagram for choosing particular sets ofacceptable droplet combinations for each target region of the substrate,usable for example with any of the embodiments introduced earlier.

FIG. 6B provides a block diagram for iteratively planning printhead/substrate motion and using of nozzles based on combinations ofdroplets for each print region.

FIG. 6C provides a block diagram that illustrates further optimizationof print head/substrate motion and the use of nozzles, specifically, toorder scans in a manner that printing can be performed as efficiently aspossible.

FIG. 6D is a hypothetical plan view of a substrate that will ultimatelyproduce multiple flat panel display devices (e.g., 683); as denoted byregion 687, print head/substrate motion can be optimized for aparticular region of a single flat panel display device, withoptimizations being used on a repeatable or periodic basis across eachdisplay device (such as the four depicted flat panel display devices).

FIG. 7 provides a block diagram for deliberately varying fill volumeswithin acceptable tolerances in order to reduce visual artifacts in adisplay device.

FIG. 8A provides a graph that shows variation in target region fillvolume without adjustments for nozzle-to-nozzle droplet volume variationof a print head.

FIG. 8B provides a graph that shows variation in target region fillvolume where different nozzles are randomly used to statisticallycompensate for nozzle-to-nozzle droplet volume variation of a printhead.

FIG. 8C provides a graph that shows variation in target region fillvolume where one or more droplets of different volumes are used toachieve target region fill volume within precise tolerances on a plannedbasis.

FIG. 9A provides a graph that shows variation in target region fillvolume without adjustments for nozzle-to-nozzle droplet volume variationof a print head.

FIG. 9B provides a graph that shows variation in target region fillvolume where different nozzles are randomly used to statisticallycompensate for nozzle-to-nozzle droplet volume variation of a printhead.

FIG. 9C provides a graph that shows variation in target region fillvolume where one or more droplets of different volumes are used toachieve target region fill volume within precise tolerances on a plannedbasis.

FIG. 10 shows a plan view of a printer used as part of a fabricationapparatus; the printer can be within a gas enclosure that permitsprinting to occur in a controlled atmosphere.

FIG. 11 provides a block diagram of a printer; such a printer can beoptionally employed for example in the fabrication apparatus depicted inFIG. 10.

FIG. 12A shows an embodiment where multiple print heads (each withnozzles) are used to deposit ink on a substrate.

FIG. 12B shows rotation of the multiple print heads to better alignnozzles of the respective print heads with the substrate.

FIG. 12C shows offset of individual ones of the multiple print heads inassociation with intelligent scanning, to deliberately produce specificdroplet volume combinations.

FIG. 12D shows a cross-section of a substrate, including layers that canbe used in an organic light-emitting diode (OLED) display.

FIG. 13A shows a number of different ways of customizing or varying anozzle firing waveform.

FIG. 13B shows a way of defining a waveform according to discretewaveform segments.

FIG. 14A shows an embodiment where different droplet volume combinationscan be achieved using different combinations of predetermined nozzlefiring waveforms.

FIG. 14B shows circuitry associated with generating and applying aprogrammed waveform at a programmed time (or position) to a nozzle of aprint head; this circuitry provides one possible implementation of eachof circuits 1423/1431, 1424/1432 and 1425/1433 from FIG. 14A, forexample.

FIG. 14C shows a flow diagram of one embodiment that uses differentnozzle firing waveforms.

The subject matter defined by the enumerated claims may be betterunderstood by referring to the following detailed description, whichshould be read in conjunction with the accompanying drawings. Thisdescription of one or more particular embodiments, set out below toenable one to build and use various implementations of the technologyset forth by the claims, is not intended to limit the enumerated claims,but to exemplify their application. Without limiting the foregoing, thisdisclosure provides several different examples of techniques used tofabricate a materials layer by planning print head movement so as tomaintain deposited ink volume within predetermined allowances while notexcessively increasing the number of print head passes (and thus thetime needed to complete a deposited layer). These techniques can beembodied as software for performing these techniques, in the form of acomputer, printer or other device running such software, in the form ofcontrol data (e.g., a print image) for forming a materials layer, as adeposition mechanism, or in the form of an electronic or other device(e.g., a flat panel device or other consumer end product) fabricated asa result of these techniques. While specific examples are presented, theprinciples described herein may also be applied to other methods,devices and systems as well.

DETAILED DESCRIPTION

This disclosure relates to use of a printing process to transfer layermaterial to a substrate. The nozzle consistency issue introduced aboveis addressed by measuring droplet volume per nozzle (or variation indroplet volume across nozzles) of a print head for a given nozzle firingwaveform. This permits planning of print head firing patterns and/ormotion to deposit precise aggregate fill volumes of ink in each targetregion. With an understanding of how droplet volume varies acrossnozzles, print head/substrate positional offsets and/or droplet firingpatterns can be planned in a manner that accommodates differences indroplet volumes but that still concurrently deposits droplets inadjacent target regions with each pass or scan. Viewed from a differentperspective, rather than normalizing or averaging out nozzle-to-nozzlevariation in droplet volumes, the specific droplet volumecharacteristics of each nozzle are measured and used in a planned mannerto concurrently achieve specific in-range aggregate volumes for multipletarget regions of the substrate; in many embodiments, this task isperformed using an optimization process that reduces the number of scansor print head passes in dependence on one or more optimization criteria.

In one optional embodiment, the print head and/or the substrate are“stepped” in variable amounts so as to change, as appropriate, thenozzle used for each target region in various passes to ejectspecifically desired droplet volumes. Multiple passes are planned sothat each target region receives a specific aggregate fill. That is,each target region (for example, each well in a row of wells that willform pixelated components of a display) receives a planned combinationof one or more droplet volumes to achieve an aggregate volume within aspecified tolerance range using different geometric steps of print headrelative to substrate. In more detailed features of this embodiment,given the nozzles' positional relationships to one another, a paretooptimal solution can be computed and applied, such that a tolerableamount of volume variation in each target region is permitted, withinspecification, but at the same time, the print head/substrate movementis planned to maximize average concurrent use of nozzles for respectivetarget deposition regions. In one optional refinement, a function isapplied to reduce and even minimize the number of print head/substratepasses needed for printing. Reflecting briefly upon these variousfeatures, fabrication cost is substantially reduced as the printing oflayers of material on a substrate can be performed quickly andefficiently.

Note that in a typical application, the target regions that receive inkcan be arrayed, that is, laid out in rows and columns, where a swathdescribed by relative print head/substrate motion will deposit ink in asubset of all of the rows (of target regions of the array), but in amanner that covers all columns of the array in a single pass; also, thenumber of rows, columns and print head nozzles can be quite large, e.g.,involving hundreds or thousands of rows, columns and/or print headnozzles.

A second optional embodiment addresses the nozzle consistency issue in aslightly different manner. A set of multiple, prearranged, alternatenozzle firing waveforms with known (and different) droplet volumecharacteristics is made available to each nozzle; for example, a set offour, eight or another number of alternate waveforms can be hard-wiredor otherwise predefined to provide a corresponding set of selectable,slightly-different droplet volumes. Per-nozzle volume data (ordifference data) is then used to plan for concurrent deposition ofmultiple target regions by determining sets of nozzle-waveformcombinations for each target region of the substrate. Once again, thespecific volume characteristics of each nozzle (and in this case, eachnozzle-waveform combination) are relied upon to achieve specific fillvolumes; that is, rather than attempting to correct per-nozzle volumevariation, the variation is specifically used in combinations to obtainspecific fill volumes. Note that there will typically be a large numberof alternate combinations that could be used to deposit droplets inreach a desired range in each target region of the substrate. In a moredetailed embodiment, a “common set” of nozzle waveforms can be sharedacross some (or even all) nozzles of a print head, with per-nozzledroplet volumes stored and available for mixing and matching differentdroplet volumes to achieve specific fills. As a further option, acalibration phase can be used to select different waveforms in anoff-line process, with a set of specific nozzle firing waveforms beingselected based on calibration to achieve a set of respective,specifically-desired volume characteristics. Once again, in furtherdetailed embodiments, optimization can be performed to plan printing ina way that improves printing time, for example, by minimizing the numberof scans or print head passes, by maximizing concurrent nozzle use, orby optimizing some other criteria.

An optional third embodiment relies on the use of multiple print headseach having nozzles that can be offset relative to one another (orequivalently, a print structure having multiple rows of nozzles that canbe offset relative to one another). Using such deliberate offset,per-nozzle volume variations can be intelligently combined across printheads (or rows of nozzles) with each pass or scan. Again, there willtypically be a large number of alternate combinations that could be usedto deposit droplets to reach a desired range in each target region ofthe substrate and, in detailed embodiments, optimization is performed toplan the use of offsets in a way that improves printing time, forexample, by minimizing the number of scans or print head passes, or bymaximizing concurrent nozzle use, and so forth.

Note that one benefit of the techniques described above is that byliving with droplet volume variations but combining them to achievespecific, predetermined target region fill volumes, one can achieve ahigh degree of control over not only the ability to satisfy a desiredfill tolerance range, but also over precise volume amounts anddeliberately controlled (or injected) variation in such amounts. Forexample, in one exemplary application of the mentioned techniques, i.e.,the fabrication of display devices, the techniques mentioned abovefacilitate controlled, deliberate variation in fill volumes frompixel-to-pixel that will obscure any display artifacts in a finisheddisplay (i.e., to mitigate “line effect” that might otherwise be visibleto the human eye in a finished, electrically-operable displays). Thatis, even a slight discrepancy in displays at low spatial frequency canintroduce unintended artifacts which are visible to the human eye andwhich are therefore undesirable. It is therefore desired in someembodiments to deliberately vary the fill volume of each target region,albeit still within specification. Using an exemplary tolerance of 49.75pL-50.25 pL, rather than simply arbitrarily ensuring that all targetregion fills are at a common, precise value within this tolerance range,it can be desired for such applications to deliberately introduce randomvariation within this range, such that any pattern of variation ordifference is not observable to the human eye as a pattern in afinished, operating display. Applied to a color display, one exemplaryembodiment deliberately adds such fill volume variation in a mannerstatistically independent for at least one of (a) an x dimension (e.g.,along the direction of a row of target regions), (b) a y dimension(e.g., along the direction of a column of target regions), and/or (c)across one or more color dimensions (e.g., independently for red versusblue, blue versus green, red versus green target regions). In oneembodiment, variation is statistically independent across each of thesedimensions. Such variation is believed to render any fill volumevariations imperceptible to the human eye and thus to contribute to highimage quality of such displays.

An example will help introduce some concepts relating to intelligentplanning of fill volumes per target region. Per-nozzle volume data (ordifference data) for a given nozzle firing waveform can be used to planfor concurrent deposition of multiple target regions by determiningpossible nozzle-droplet volume sets for each target region. There willtypically be a large number of possible combinations of nozzles that candeposit ink droplets in multiple passes to fill each target region to adesired fill volume within a narrow tolerance range that meetsspecification. Returning briefly to the hypothetical introduced usingFIG. 1A, if acceptable fill volumes according to specification werebetween 49.75 pL and 50.25 pL (i.e., within a range of 0.5% of target),acceptable fill volumes could also be achieved using many different setsof nozzles/passes, including without limitation: (a) five passes ofnozzle 2 (10.01 pL) for a total of 50.05 pL; (b) a single pass of nozzle1 (9.80 pL) and four passes of nozzle 5 (10.03 pL), for a total of 49.92pL; (c) a single pass of nozzle 3 (9.89 pL) and four passes of nozzle 5(10.03 pL), for a total of 50.01 pL; (d) a single pass of nozzle 3 (9.89pL), three passes of nozzle 4 (9.96 pL), and a single pass of nozzle 5(10.03 pL) for a total of 49.80 pL; and (e) a single pass of nozzle 2(10.01 pL), two passes of nozzle 4 (9.96 pL) and two passes of nozzle 5(10.03 pL) for a total of 49.99 pL. Other combinations are clearly alsopossible. Thus, even if only one choice of nozzle drive waveform wasavailable for each nozzle (or all nozzles), the first embodimentintroduced above can be used to offset the print head relative to thesubstrate in a series of planned offsets or “geometric steps” that applyas many nozzles as possible during each scan to deposit droplets (e.g.,in different target regions), but that combine deposited droplets foreach target region in a specifically-intended manner. That is, manycombinations of nozzle-droplet volumes in this hypothetical could beused to achieve desired fill volumes, and a specific embodimenteffectively selects a particular one of the acceptable dropletcombinations for each target region (i.e., a particular set for eachregion) through its selection of scanning motion and/or nozzle drivewaveforms, so as to facilitate concurrent fills of different rows and/orcolumns of target regions using respective nozzles. By choosing thepattern of relative print head/substrate motion in a way that minimizesthe time over which printing occurs, this first embodiment provides forsubstantially-enhanced manufacturing throughput. Note that thisenhancement can optionally be embodied in the form of minimizing thenumber of print head/substrate scans or “passes,” in a manner thatminimizes the raw distance of relative print head/substrate movement orin a manner that otherwise minimizes overall printing time. That is tosay, the print head/substrate movement (e.g., scans) can be preplannedand used to fill target regions in a manner that meets predefinedcriteria, such as minimal print head/substrate passes or scans, minimalprint head and/or substrate movement in a defined dimension ordimension(s), printing in a minimal amount of time, or other criteria.

The same approaches all apply equally to the hypothetical of FIG. 1B inwhich the nozzles are not specially aligned to respective targetregions. Again, if acceptable fill volumes according to specificationwere between 49.75 pL and 50.25 pL (i.e., within a range of 0.5% ofeither side of target), acceptable fill volumes could also be achievedmany different sets of nozzles/passes, including without limitation, allof the examples listed above for FIG. 1A as well as additional examplesparticular to the hypothetical of FIG. 1B in which two adjacent nozzlesare used in a single pass to fill a particular target region, forexample, two passes of nozzle (4) (9.96 pL) and of nozzle (5) (10.03pL), and one pass of nozzle (2) (10.01 pL) for a total of 49.99 pL.Other combinations are clearly also possible.

These same principles also apply to the second embodiment introducedabove. For example, in the hypothetical presented by FIG. 1A, each ofthe nozzles can be driven by five different firing waveforms, identifiedas firing waveforms A through E, such that the resulting volumecharacteristics of the different nozzles for the different firingwaveforms are described by Table 1A, below. Considering only targetregion 104 and only nozzle (1), it would be possible to deposit the50.00 pL target in five passes, for example, with a first print headpass using predefined firing waveform D (to generate from nozzle (1) a9.96 pL droplet), and with four subsequent passes using predefinedfiring waveform E (to generate from nozzle (1) a 10.01 pL droplet), allwithout any offset in scan path. Similarly, different combinations offiring waveforms can be used concurrently in each pass for each nozzleto generate volumes in each of the target regions that is close to thetarget values without any offset in scan path. Therefore, using multiplepasses in this manner would be advantageous for embodiments where it isdesired to concurrently deposit droplets in different target regions(i.e., in different rows of pixels for example).

TABLE 1A Nozzle Waveform (1) (2) (3) (4) (5) A 9.80 10.01 9.89 9.9610.03 B 9.70 9.90 9.81 9.82 9.94 C 9.89 10.10 9.99 10.06 10.13 D 9.9610.18 10.07 10.15 10.25 E 10.01 10.23 10.12 10.21 10.31

These same approaches all apply equally to the hypothetical of FIG. 1B.For example, considering only target region 104 and nozzles (1) and (2)(i.e. the two nozzles that overlap target region 154 during a scan), itis possible to achieve 50.00 pL in three passes, for example, with afirst print head pass using nozzle (1) and predefined waveform B (for adroplet volume of 9.70 pL) and nozzle (2) and predefined waveform C (fora droplet volume of 10.10), a second print head pass using nozzle (1)and predefined waveform E (for a droplet volume of 10.01 pL) and nozzle(2) and predefined waveform D (for a droplet volume of 10.18 pL), and athird print head pass using nozzle (1) and predefined waveform E (for adroplet volume of 10.01 pL.)

Note that it would also likely be possible for both the hypothetical ofFIG. 1A and the hypothetical of FIG. 1B to deposit each fill each targetvolume in a single row of target regions in this example in a singlepass; for example, it would be possible to rotate the print head byninety degrees and deposit exactly 50.00 pL with a single droplet fromeach nozzle for each target region in a row, for example, using waveform(E) for nozzle (1), waveform (A) for nozzles (2), (4) and (5) andwaveform (C) for nozzle (3) (10.01 pL+10.01 pL+9.99 pL+9.96 pL+10.03pL=50.00 pL).

These same principles also apply to the third embodiment introducedabove. For example, for the hypothetical presented by FIG. 1A, thevolume characteristics can reflect the nozzles for a first print head(e.g., “print head A”), with this first print head being integratedtogether with four additional print heads (e.g., print heads “B” through“E”), each being driven by a single firing waveform and havingrespective per-nozzle droplet volume characteristics. The print headsare collectively organized such that in executing a scan pass each ofthe nozzles identified as nozzle (1) for a print head is aligned toprint into a target region (e.g., target region 104 from FIG. 1A), eachof the nozzles identified as nozzle (2) from the various print heads arealigned to print into a second target region (e.g., target region 105from FIG. 1A), and so on, with the volume characteristics of thedifferent nozzles for the different print heads are described by Table1B, below. Optionally, the respective print heads can be offset from oneanother using a motor that adjusts spacing, e.g., in between scans.Considering only target region 104 and the nozzle (1) on each printhead, it would be possible to deposit the 50.00 pL in a four passes, forexample, with a first print head pass in which print head D and printhead E both fire a droplet into the target region, and three subsequentpasses in which only print head E fires a droplet into the targetregion. Other combinations are possible using even fewer passes that canstill generate volumes in the target region close to the 50.00 pLtarget, for example, within a range of 49.75 pL and 50.25 pL.Considering again only target region 104 and the nozzle (1) on eachprint head, it would be possible to deposit 49.83 pL in two passes, forexample, with a first print head pass in which print heads C, D, and Eall fire a droplet into the target region, and a second print head passin which print heads D and E both fire a droplet into the target region.Similarly, different combinations of nozzles from different print headscan be used concurrently in each pass to generate volumes in each of thetarget regions that is close to the target values without any offset inscan path. Therefore, using multiple passes in this manner would beadvantageous for embodiments where it is desired to concurrently depositdroplets in different target regions (i.e., in different rows of pixelsfor example).

TABLE 1B Nozzle Print head (1) (2) (3) (4) (5) A 9.80 10.01 9.89 9.9610.03 B 9.70 9.90 9.81 9.82 9.94 C 9.89 10.10 9.99 10.06 10.13 D 9.9610.18 10.07 10.15 10.25 E 10.01 10.23 10.12 10.21 10.31

All of the same approaches apply equally to the hypothetical of FIG. 1B.Again considering only target region 154 and the nozzles (1) and (2) oneach print head (i.e. the nozzles that overlap with target region 154during a scan), it is possible to deposit 50.00 pL in two passes, forexample, with a first print head pass in which print heads C and E firenozzle (1) and print heads B and C fire nozzle (2), and a second printhead pass in which print head C fires nozzle (2). It is also possible todeposit 49.99 pL (clearly within an example target range of 49.75 pL and50.25 pL) in a single pass, for example, with a print head pass in whichprint heads C, D, and E fire nozzle (1) and print heads B and E firenozzle (2).

It should also be apparent that, optionally combined with scan pathoffsets, the use of alternate nozzle firing waveforms dramaticallyincreases the number of droplet volume combinations that can be achievedfor a given print head, and these options are yet further increased bythe use of multiple printheads (or equivalently, multiple rows ofnozzles) as described above. For example, in the hypothetical exampleconveyed by the discussion of FIG. 1 above, a combination of fivenozzles with respective inherent ejection characteristics (e.g., dropletvolumes) and eight alternate waveforms could provide literally manythousands of different sets of possible droplet volume combinations.Optimizing sets of nozzle-waveform combinations, and selecting aparticular set of nozzle-waveform combinations for each target region(or for each row of print wells in an array) enables furtheroptimization of printing according to the desired criteria. Inembodiments that use multiple print heads (or rows of print headnozzles), the ability to selectively offset those print heads/rows alsofurther enhances the number of combinations that can be applied perprint head/substrate scan. Once again, for these embodiments, given thatmultiple sets (of one or more) nozzle-waveform combinations canalternatively be used to achieve specified fill volumes, this secondembodiment selects a particular one of the “acceptable” sets for eachtarget region, with this selection of the particular one across targetregions generally corresponding to the concurrent printing of multipletarget regions using multiple nozzles. That is, by varying parameters tominimize the time over which printing occurs, these embodiments eachenhance manufacturing throughput, and facilitate minimizing the numberof required print head/substrate scans or “passes,” the raw distance ofrelative print head/substrate movement along a particular dimension(s),overall printing time, or that help satisfy some other predeterminedcriteria.

Note that these techniques are optional relative to one another; thatis, for example, it is possible to use multiple nozzle-firing waveformsto achieve desired droplet combinations without varying positional stepof print head/substrate scans and without offsetting multiple printheads/nozzle rows, and it is possible to use print head/nozzle rowoffsets without varying positional steps or varying nozzle firingwaveforms.

These various techniques can also optionally be combined in any desiredmanner with each other or with other techniques. For example, it ispossible to “tune” the nozzle drive waveform on a per-nozzle basis toreduce variation in per-nozzle droplet volumes (e.g., shaping of thedrive pulse, by changing drive voltage, rise or fall slopes, pulsewidth, decay time, number and respective levels of pulses used perdroplet, and so forth).

While certain applications discussed in this document refer to fillvolumes in discrete fluid receptacles or “wells,” it is also possible touse the mentioned techniques to deposit a “blanket coating” having largegeographies relative to other structures of the substrate (e.g., such asrelative to transistors, pathways, diodes and other electroniccomponents). In such a context, fluidic ink carrying layer materials(e.g., that will be cured, dried or hardened in situ to form a permanentdevice layer) will spread to a certain extent, but will (given inkviscosity and other factors) still retain specific characteristicsrelative to other target deposition regions of the substrate. It ispossible to use the techniques herein in this context, for example, todeposit blanket layers such as encapsulation or other layers withspecific, localized control over ink fill volumes for each targetregion. The techniques discussed herein are not limited by thespecifically-presented applications or embodiments.

Other variations, advantages and applications from the techniquesintroduced above will be readily apparent to those skilled in the art.This is to say, these techniques can be applied to many different areasand are not limited to the fabrication of display devices or pixelateddevices. A print “well” as used herein refers to any receptacle of asubstrate that is to receive deposited ink, and thus has chemical orstructural characteristics adapted to constrain the flow of that ink. Aswill be exemplified for OLED printing below, this can include situationswere respective fluid receptacles are to each receive a respectivevolume of ink and/or a respective type of ink; for example, in a displayapplication where the mentioned techniques are used to deposit lightemitting materials of different colors, successive printing processescan be performed for each color, using respective print heads andrespective inks—in this case, each process could deposit “every thirdwell” in an array (e.g., for every “blue” color component), orequivalently, every well in a third array (which intersperses wells withoverlapping arrays for other color components). Other variations arealso possible. Note also that “rows” and “columns” are used in thisdisclosure without implying any absolute direction. For example, a “row”of print wells could extend the length of or width of a substrate, or inanother manner (linear or non-linear); generally speaking, “rows” and“columns” will be used herein to refer to directions that each representat least one independent dimension, but this need not be the case forall embodiments. Also, note that because modern printers can userelative substrate/print head motion that involves multiple dimensions,relative movement does not have to be linear in path or speed, which isto say, print head/substrate relative motion does not have to follow astraight or even a continuous path or constant velocity. Thus, a “pass”or “scan” of a print head relative to a substrate simply refers to aniteration of depositing droplets using multiple nozzles over multipletarget regions that involves relative print head/substrate motion. Inmany embodiments described below for a OLED printing process, however,each pass or scan can be a substantially continuous, linear motion, witheach ensuing pass or scan being parallel to the next, offset by ageometric step relative to one another. This offset, or geometric stepcan be a difference in pass or scan starting position, average position,finishing position, or some other type of positional offset, and doesnot imply necessarily parallel scan paths. It is also noted that variousembodiments discussed herein speak of “concurrent” use of differentnozzles to deposit in different target regions (e.g., different rows oftarget regions); this term “concurrent” does not require simultaneousdroplet ejection, but rather, merely refers to the notion that duringany scan or pass, different nozzles or groups of nozzles can be used tofire ink into respective target regions on a mutually-exclusive basis.For example, a first group of one or more nozzles can be fired during agiven scan to deposit first droplets in a first row of fluid wells,while a second group of one or more nozzles can be fired during thissame given scan to deposit second droplets into a second row of fluidwells.

With principal parts of several different embodiments thus laid out,this disclosure will be roughly organized as follows. FIGS. 2A-3C willbe used to introduce some general principles relating to the nozzleconsistency issue, OLED printing/fabrication, and how embodimentsaddress the nozzle consistency issue. These FIGS. will also be used tointroduce concepts relating to planning print head/substrate motion, forexample, where offset variation is used to change which print headnozzles are used to deposit droplets in each row of an array of targetregions of a substrate. FIGS. 4-7 will be used to exemplify softwareprocesses that can be used to plan droplet combinations for each targetregion of the substrate. FIGS. 8A-9C are used to present some empiricaldata, that is, which demonstrates effectiveness of the mentionedtechniques in improving well fill consistency. FIGS. 10-11 will be usedto discuss an exemplary application to OLED panel fabrication, andassociated printing and control mechanisms. FIGS. 12A-12C are used todiscuss print head offsets that can be used to vary droplet combinationsthat can be deposited with each scan. Finally, FIGS. 13A-14C are used tofurther discuss different, alternate nozzle firing waveforms, applied toprovide for different droplet volumes.

As represented by FIG. 2A, in one application, a printing process can beused to deposit one or more layers of material onto a substrate. Thetechniques discussed above can be used to generate printer controlinstructions (e.g., an electronic control file that can be transferredto a printer) for subsequent use in fabricating a device. In onespecific application, these instructions can be geared for an inkjetprinting process useful in printing a layer of a low-cost, scalableorganic light-emitting diode (“OLED”) display. More specifically, thementioned techniques can be applied to deposit one or morelight-emitting or other layers of such an OLED device, for example,“red” “green” and “blue” (or other) pixelated color components or otherlight-emitting layers or components of such a device. This exemplaryapplication is non-limiting, and the mentioned techniques can be appliedto fabrication of many other types of layers and/or devices, whether ornot those layers are light-emitting and whether or not the devices aredisplay devices. In this exemplary application, various conventionaldesign constraints of inkjet print heads provide challenges to theprocess efficiency and film coating uniformity of various layers of anOLED stack that can be printed using various inkjet printing systems.Those challenges can be addressed through the teachings herein.

More specifically, FIG. 2A is a plan view of one embodiment of a printer201. The printer includes a print head 203 that is used to depositfluidic ink onto a substrate 205. Unlike printer applications that printtext and graphics, the printer 201 in this example is used in amanufacturing process to deposit fluidic ink that will have a desiredthickness. That is, in a typical manufacturing application, the inkcarries a material that will be used to form a permanent layer of afinished device, where that layer has a specifically-desired thicknessdependent on the volume of applied ink. The ink typically features oneor more materials that will form part of the finished layer, formed asmonomer, polymer, or a material carried by a solvent or other transportmedium. In one embodiment, these materials are organic. Followingdeposition of the ink, the ink is dried, cured or hardened to form thepermanent layer; for example, some applications use an ultraviolet (UV)cure process to convert a monomer or polymer into a hardened material,while other processes dry the ink to remove the solvent and leave thetransported materials in a permanent location. Other processes are alsopossible. Note that there are many other variations that differentiatethe depicted printing process from conventional graphics and textapplications; for example, in some embodiments, deposition of thedesired materials layers is performed in an environment controlled toeither regulate the ambient atmosphere to be something other than air,or otherwise to exclude unwanted particulates. For example, as will bedescribed further below, one contemplated application uses a fabricationmechanism that encloses the printer 201 within a gas chamber, such thatprinting can be performed in the presence of a controlled atmospheresuch as an inert environment including, for example, but not limited by,nitrogen, any of the noble gases, and any combination thereof.

As further seen in FIG. 2A, the print head 203 includes a number ofnozzles, such as nozzle 207. Note that in FIG. 2A, for ease ofillustration, the print head 203 and nozzles are depicted as opening outof the top of the page, but in fact, these nozzles and print head facedownward toward the substrate and are hidden from view from theperspective of FIG. 2A (i.e., FIG. 2A shows what in effect is a cut-awayview of the print head 203). The nozzles are seen to be arranged in rowsand columns (such as exemplary row 208 and column 209), although this isnot required for all embodiments, i.e., some implementations use only asingle row of nozzles (such as row 208). In addition, it is possible forrows of nozzles to be disposed on respective print heads, with eachprint head being (optionally) individually offsettable relative to oneanother, as introduced above. In an application where the printer isused to fabricate part of a display device, for example, materials foreach of respective red, green and blue color components of a displaydevice, the printer will typically use dedicated print head componentsfor each different ink or material, and the techniques discussed hereincan be separately applied to each corresponding print head.

FIG. 2A illustrates one print head 203. The printer 201 includes in thisexample two different motion mechanisms that can be used to position theprint head 203 relative to the substrate 205. First, a traveler orcarriage 211 can be used to mount the print head 203 and to permitrelative motion as denoted by arrows 213. Second, however, a substratetransport mechanism can be used to move the substrate relative to thetraveler, along one or more dimensions. For example, as denoted byarrows 215, the substrate transport mechanism can permit movement ineach of two orthogonal directions, such as in accordance with x and yCartesian dimensions (217), and can optionally support substraterotation. In one embodiment, the substrate transport mechanism comprisesa gas floatation table used to selectively secure and permit movement ofthe substrate on a gas bearing. Note further that the printer optionallypermits rotation of the print head 203 relative to the traveler 211, asdenoted by rotation graphic 218. Such rotation permits the apparentspacing and relative configuration of the nozzles 207 to be changedrelative to the substrate; for example, where each target region of thesubstrate is defined to be a specific area, or to have a spacingrelative to another target region, rotation of the print head and/or thesubstrate can change the relative separation of the nozzles in adirection along or perpendicular to a scan direction. In an embodiment,the height of the print head 203 relative to the substrate 205 can alsobe changed, for example, along a z Cartesian dimension that is into andout of the direction of view of FIG. 2A.

Two scan paths are respectively illustrated by directional arrows 219and 220 in FIG. 2A. Briefly, the substrate motion mechanism moves thesubstrate back and forth in the direction of arrows 219 and 220 as theprint head moves in geometric steps or offsets in the direction ofarrows 213. Using these combinations of movements, the nozzles of theprint head can reach any desired region of the substrate to deposit ink.As referenced earlier, the ink is deposited on a controlled basis intodiscrete target regions of the substrate. These target regions can bearrayed, that is, arranged in rows and columns such as optionally alongthe depicted y and x dimensions, respectively. Note that the rows ofnozzles (such as row 208) are seen in this FIG. perpendicular to therows and columns of target regions, i.e., such that a row of nozzlessweeps with each scan along the direction of rows of target regions,traversing each of the columns of target regions of the substrate (forexample, along direction 219). This need not be the case for allembodiments. For efficiency of motion, the subsequent scan or pass thenreverses this direction of motion, hitting the columns of target regionsin reverse order, that is, along direction 220.

Arrangement of the target regions in this example is depicted by ahighlighted region 221, which is seen in expanded view to the right sideof the FIG. That is, two rows of pixels, each pixel having red, greenand blue color components, are each represented by numeral 223, whereascolumns of pixels orthogonal to the scan direction (219/220) are eachrepresented by numeral 225. In the upper left-most pixel, the red, greenand blue color components are seen to occupy distinct target regions227, 229 and 231 as part of respective, overlapping arrays of regions.Each color component in each pixel can also have associated electronics,for example as represented by numeral 233. Where the device to befabricated is a backlit display (for example, as part of aconventional-type LCD television), these electronics can controlselective generation of light that is filtered by the red, green andblue regions. Where the device to be fabricated is a newer type display,that is where red, green and blue regions directly generate their ownlight having corresponding color characteristics, these electronics 233can include patterned electrodes and other material layers thatcontribute to the desired light generation and light characteristics.

FIG. 2B provides a close-up, cross-sectional view of the print head 203and substrate 205, taken from the perspective of lines A-A in FIG. 2A.In FIG. 2B, numerals already introduced in reference to FIG. 2Arepresent the same features. More specifically, numeral 201 generallydenotes the printer, while numeral 208 represents a row of print nozzles207. Each nozzle is designated using a parenthetical number, e.g., (1),(2), (3), etc. A typical print head typically has plural such nozzles,for example, 64, 128 or another number; in one embodiment, there can beover 1,000 nozzles, arranged in one or more rows. As noted earlier, theprint head in this embodiment is moved relative to the substrate toeffectuate geometric steps or offsets between scans, in the directionreferenced by arrows 213. Depending on the substrate motion mechanism,the substrate can be moved orthogonal to this direction (e.g., into andout of the page, relative to the view of FIG. 2B) and in someembodiments, also in the direction represented by arrows 213. Note thatFIG. 2B also shows a column 225 of respective target regions 253 of thesubstrate, in this case, arranged as “wells” that will receive depositedink and retain the deposited ink within structural confines of therespective well. It will be assumed for purposes of FIG. 2B that onlyone ink is represented (e.g., each depicted well 253 represents only onecolor of a display, such as the red color component, with other colorcomponents and associated wells not being shown). Note that the drawingis not true to scale, e.g., the nozzles are seen to be numbered from (1)to (16) while the wells are seen to be lettered from (A) to (ZZ),representing 702 wells. In some embodiments, the nozzles will align torespective wells, such that the depicted print head with 16 nozzleswould deposit ink in the direction of arrows 255 in as many as 16 wellsat the same time using scans of relative print head/substrate motionthat are into and out of the page from the perspective of FIG. 2B. Inother embodiments, as mentioned (e.g., with reference to FIG. 1B),nozzle density will be much greater than target region density, and withany scan or pass, a subset of nozzles (e.g., a group of one to many,dependent on which nozzles traverse each target region) will be used fordeposition. For example, again using an illustrative example of sixteennozzles, it could be that nozzles (1)-(3) can be used to deposit ink ina first target region and nozzles (7-10) can be concurrently used todeposit ink in a second target region, on a mutually-exclusive basis forthe given pass.

Conventionally, a printer might be operated to use sixteen nozzles toconcurrently deposit ink in as many as sixteen rows of wells, movingback and forth with ensuing scans as necessary, until e.g. five dropletswere deposited in each well, with the print head being advanced asnecessary using a fixed step that is an integer multiple of a width ofthe swath traversed by the scan. The techniques provided by thisdisclosure, however, make use of the inherent variation in dropletvolumes produced by different nozzles, in combinations calculated toproduce a specific fill volume for each well. Different embodiments relyon different techniques to achieve these combinations. In oneembodiment, the geometric step is varied to achieve the differentcombinations, and is free to be something other than an integer multipleof the width described by the print head swath. For example, ifappropriate to depositing selected sets of droplet combinations in therespective wells 253 of FIG. 2A, the geometric step could be 1/160^(th)of the swath of the print head, in effect, representing a relativedisplacement between print head and substrate of a spacing of one tenthof a one row of wells in this example. The next offset or geometric stepcould be different, as appropriate to the particular combination ofdroplets desired in each well, for example, a hypothetical offset of5/16^(ths) of the print head swath, corresponding to an integer spacingof wells; this variation could continue with both positive and negativesteps as necessary to deposit ink to obtain the desired fill volumes.Note that many different types or sizes of offsets are possible and thatstep size need not be fixed from scan-to-scan or be a specific fractionof well spacing. In many manufacturing applications, however, it isdesired to minimize printing time, in order to maximize rate ofproduction and minimize per-unit manufacturing costs as much aspossible; to this end, in specific embodiments, print head motion isplanned and sequenced in a manner to minimize the total number of scans,the total number of geometric steps, the size of offsets or geometricsteps, and the cumulative distance traversed by the geometric steps.These or other measures can be used individually, together, or in anydesired combination to minimize total printing time. In embodimentswhere independently offsettable rows of nozzles are used (e.g., multipleprint heads), the geometric step can be expressed in part by the offsetbetween print heads or nozzle rows; such offset, combined with overalloffset of the print head component (e.g., a fixed step for a print headassembly) can be used to effectuate variable-size geometric steps andthus deposit droplet combinations into each well. In embodiments wherevariation in nozzle drive waveform is used alone, conventional, fixedsteps can be used, with droplet volume variation effectuated usingmultiple print heads and/or multiple print head passes. As will be notedbelow, in one embodiment, nozzle drive waveforms can be programmed foreach nozzle in between droplets, thus permitting each nozzle to produceand contribute respective droplet volumes per well within a row ofwells.

FIGS. 3A, 3B, and 3C are used to provide additional detail regardingreliance on specific droplet volumes in achieving desired fill volumes.

FIG. 3A presents an illustrative view 301 of a print head 303 and tworelated diagrams seen below the print head 303. The print head isoptionally used in an embodiment that provides non-fixed geometric stepsof print head relative to substrate, and so numeral 305 is used todenote offsets that align specific print head nozzles (e.g., 16 totalnozzles with nozzles (1)-(5) depicted in the FIG.) with different targetregions (five in this example, 307, 308, 309, 310 and 311). Harkeningback to the example of FIG. 1A, if nozzles (1)-(16) respectively producedroplet volumes of 9.80, 10.01, 9.89, 9.96, 10.03, 9.99, 10.08, 10.00,10.09, 10.07, 9.99, 9.92, 9.97, 9.81, 10.04 and 9.95 pL of fluidic ink,and if it is desired to deposit 50.00 pL per target region, ±0.5 percentof this value, the print head could be used to deposit droplets in fivepasses or scans, respectively using geometric steps of 0, −1, −1, −2 and−4, resulting in total fill values per region of 49.82, 49.92, 49.95,49.90 and 50.16 pL, as depicted in the FIG; this is clearly within thedesired tolerance range of 49.75-50.25 pL for each of the depictedtarget regions. Every step in this example is expressed on anincremental basis relative to previous position, although it is possibleto use other measures as well. Thus, as seen, the combining of dropletsin a deliberate manner that depends on respective droplet volumes andthe desired fill for each target region can be used to achieve precise,regulated fills, with a high degree of reliability.

Note that this same FIG. can be used to represent nozzle drive waveformvariation and/or the use of multiple print heads. For example, if thenozzle references (1)-(16) refer to droplet volumes for a single nozzleproduced by sixteen different drive waveforms (i.e., using waveforms1-16), the per-region fill volumes can in theory be obtained simply byusing different drive waveforms, for example, waveform nos. 1, 2, 3, 5and 9 for target region 307. In practice, since process variations canresult in different per-nozzle characteristics, the system would measuredroplet volumes for each nozzle for each waveform, and wouldintelligently plan droplet combinations on this basis. In an embodimentwhere the nozzle references (1)-(15) refer to multiple print heads(e.g., references (1)-(5) referring to a first print head, references(6)-(10) referring to a second print head and references (11)-(15)referring to a third print head), offsets between print heads can beused to reduce the number of passes or scans; for example, theright-most target region 311 could have three droplets deposited in onepass, including droplet volumes of 10.03, 10.09 and 9.97 pL (print head(1), 0 offset; print head (2), +1 offset; and print head (3), +2offset). It should be apparent that the combination of these varioustechniques facilitates many possible combinations of specific volumedroplets to achieve specific fill volumes within a tolerance range. Notein FIG. 3A that the variance in the aggregate ink fill volumes amongsttarget regions is small and within tolerance, i.e., within a range of49.82 pL to 50.16 pL.

FIG. 3B shows another illustrative view 351, with each scan representedby a different rectangle or bar, such as referenced by numerals 353-360.In connection with this FIG., it should be assumed print head/substraterelative motion is advanced in a sequence of variable-size geometricsteps. Note again that, typically, each step will designate a scan thatsweeps multiple columns of target regions (e.g., pixels) beyond a singlecolumn of five regions represented on the plane of the drawing page (andrepresented by numerals 362-366). Scans are shown in order fromtop-to-bottom, including a first scan 353 where the print head is seendisplaced to the right relative to the substrate, such that only nozzles(1) and (2) are aligned with target regions 365 and 366, respectively.Within each print scan depiction (such as box 353), circles representeach nozzle either with a solid black fill, to denote that the nozzle isto be fired when that nozzle is over the specifically-depicted targetregion during the scan, or “hollow,” that is, with a white fill, todenote that the nozzle is not to be fired at the pertinent time (but maybe for other target regions encountered on the scan). Note that, in thisembodiment, each nozzle is fired on a binary basis, i.e., each nozzle iseither fired or not according to any adjustable parameters, e.g., todeposit for each target region encountered during the scan apredetermined droplet volume. This “binary” firing scheme can optionallybe employed for any of the embodiments described herein (that is, e.g.,in embodiments where multiple firing waveforms are used, with waveformparameters being adjusted in between droplets). In the first pass 353,it is seen that nozzle (1) is fired to deposit a 9.80 pL droplet intothe second-to-right-most target region while nozzle (2) is fired todeposit a 10.01 pL droplet into right-most target region 366. The scancontinues to sweep other columns of target regions (e.g., other rows ofpixel wells), depositing ink droplets as appropriate. After the firstpass 353 is completed, the print head is advanced by a geometric step of−3, which moves the print head left relative to the substrate, such thatnozzle (1) will now traverse target region 362 during a second scan 354in a direction opposite to the first scan. During this second scan 354,nozzles (2), (3), (4) and (5) will also respectively traverse regions363, 364, 365 and 366. It is seen by the black-filled circles that, atthe appropriate time, nozzles (1), (2), (3) and (5) will be fired torespectively deposit droplet volumes of 9.80 pL, 10.01 pL, 9.89 pL and10.03 pL, corresponding to inherent characteristics of nozzles (1), (2),(3) and (5). Note also that in any one pass, the nozzles in a row ofnozzles used to deposit ink will do so on a mutually-exclusive basisinto respective target regions, e.g., for pass 354, nozzle (1) is usedto deposit ink into target region 362 (but none of target regions363-366), nozzle (2) is used to deposit ink in target region 363 (butnone of regions 362 or 364-366), nozzle (3) is used to deposit ink intarget region 364 (but none of regions 362-363 or 365-366) and nozzle(5) is used to deposit ink in target region 366 (but none of regions362-365). A third scan, denoted using numeral 355, advances the printhead effectively by one row of target regions (−1 geometric step), suchthat nozzles (2), (3), (4), (5) and (6) will traverse regions 362, 363,364, 365 and 366, respectively during the scan; solid-fill nozzlegraphics denote that during this pass, each of nozzles (2)-(6) will beactuated to fire droplets, respectively producing volumes of 10.01,9.89, 9.96, 10.03 and 9.99 pL.

If the print process was stopped at this point in time, region 366 wouldfor example have a fill of 30.03 pL (10.01 pL+10.03 pL+9.96 pL)corresponding to three droplets, whereas region 362 would have a fill of19.81 pL (9.80 pL+10.01 pL), corresponding to two droplets. Note thatthe scan pattern in one embodiment follows the back and forth patternrepresented by arrows 219 and 220 of FIG. 2A. Ensuing passes 356, 357,358, 359, 360 and 361 of these target regions (or scans of multiplecolumns of multiple such regions) respectively deposit: (a) 10.01 pL,0.00 pL, 0.00 pL, 10.08 pL and 10.09 pL droplets in region 362,corresponding to passes by nozzles (2), (3), (4), (7) and (9) insuccessive scans; (b) 0.00 pL, 0.00 pL, 10.03 pL, 10.00 pL and 10.07 pLdroplets in region 363, corresponding to respective passes by nozzles(3), (4), (5), (8) and (10) in successive scans; (c) 9.89 pL, 9.96 pL,10.03 pL, 9.99 pL, 10.09 pL and 0.00 pL droplets in region 364,corresponding to passes by nozzles (4), (5), (6), (9) and (11) insuccessive scans; (d) 0.00 pL, 9.99 pL, 10.08 pL, 10.07 pL and 0.00 pLdroplets in region 365, corresponding to passes by nozzles (5), (6),(7), (10) and (12) in successive scans; and (e) 9.99 pL, 0.00 pL, 10.00pL, 0.00 pL and 0.00 pL droplets in region 366, corresponding to passesby nozzles (6), (7), (8), (11) and (13) in successive scans. Again, notethat nozzles in this example are used with only a single firing waveform(i.e., such that their droplet volume characteristics do not change fromscan to scan) and on a binary basis, e.g., in the fifth scan 357, nozzle(7) is not fired, producing no droplet (0.00 pL) for region 366, whileon the ensuing scan, it is fired, producing a 10.08 pL droplet forregion 365.

As seen in a graph at the bottom most portion of the page, thishypothetical scanning process produces aggregate fills of 49.99 pL,50.00 pL, 49.96 pL, 49.99 pL and 50.02 pL, easily within the desiredrange of a target value (50.00 pL) plus or minus ½ percent (49.75pL-50.25 pL). Note that in this example, nozzles were used to depositink into multiple target regions on a generally concurrent basis foreach scan, with particular combinations of droplet volumes for eachdepicted region (i.e., as identified by the graphics at numerals 362,363, 364, 365 and 366) planned so that multiple droplets could bedeposited in each target region with many of the passes. The eightdepicted passes together correlate with particular sets (or a particularcombination) of droplet volumes that produce a fill volume within thespecified tolerance range (for example, combinations of droplets fromnozzles (1), (2), (2), (7) and (9) in the case of region 362), but othersets of possible droplets could have been also possibly used. Forexample, for region 362, it would have alternatively been possible touse five droplets from nozzle (2) (5×10.01 pL=50.05 pL); thisalternative would have been inefficient, however, as additional scanswould have been required because (for example) nozzle (3) (9.89 pL)could not have been extensively used on a concurrent basis during thistime (i.e., the result from five droplets from this nozzle would havebeen 5×9.89=49.45 pL, outside the desired tolerance range). In theexample relayed by FIG. 3B, the particular scans and their sequence werechosen so as to use less print time, a smaller number of passes, smallergeometric steps and potentially small aggregate geometric step distance,or according to some other criteria. Note that the depicted example isused for narrative discussion only, and that it might be possible tofurther reduce the number of scans using the presented droplet volumesto fewer than eight scans to obtain target fill. In some embodiments,the scan process is planned in a manner that avoids a worst-casescenario with the number of scans required (e.g., one scan per row oftarget regions with the print head rotated by ninety degrees). In otherembodiments, this optimization is applied to a degree based on one ormore maximums or minimums, for example, planning scans in a manner thatresults in the fewest number of scans possible given all possibledroplet combinations for each target region for a given ink.

FIG. 3C presents an illustrative view 301 of a print head 303 and tworelated diagrams seen below the print head 303, in analogy to FIG. 3A,but here having nozzles that are not specially aligned to specificwells. The print head is optionally used in an embodiment that providesnon-fixed geometric steps of print head relative to substrate, and sonumeral 305 is used to denote offsets that align specific print headnozzles (e.g., 16 total nozzles with nozzles (1)-(5) depicted in theFIG.) with different target regions (two in this example, 374 and 375).Following again the hypothetical of FIG. 3A, if nozzles (1)-(16)respectively produce droplet volumes of 9.80, 10.01, 9.89, 9.96, 10.03,9.99, 10.08, 10.00, 10.09, 10.07, 9.99, 9.92, 9.97, 9.81, 10.04 and 9.95pL of fluidic ink, and if it is desired to deposit 50.00 pL per targetregion, ±0.5 percent of this value, the print head could be used todeposit droplets in three passes or scans, respectively using geometricsteps of 0, −1, and −3, and firing one or two drops into each targetregion per scan. This would result in total fill values per region of49.93 and 50.10, as depicted in the FIG, which is again clearly withinthe desired tolerance range of 49.75-50.25 pL for each of the depictedtarget regions. Thus, as seen, the same approach applies equally to thecase of nozzles that are not aligned to the wells, and combining ofdroplets in a deliberate manner that depends on respective dropletvolumes and the desired fill for each target region can be used toachieve precise, regulated fills. Furthermore, just as described abovefor the hypothetical of FIG. 3A, this same FIG. can be used to representnozzle drive waveform variation and/or the use of multiple print heads.For example, if the nozzle references (1)-(16) refer to droplet volumesfor a single nozzle produced by sixteen different drive waveforms (i.e.,using waveforms 1-16), the per-region fill volumes can in theory beobtained simply by using different drive waveforms. One of ordinaryskill in the art can see that the same approaches as described abovewith reference to FIG. 3B also applies equally to the case of nozzlesthat are not specially aligned to the wells, i.e., with groups of one ormore nozzles being used for concurrent droplet deposition intorespective wells. Note finally that FIGS. 3A, 3B, and 3C also representrelatively simple examples; in a typical application, there may behundreds to thousands of nozzles, and millions of target regions. Forexample, in an application where the disclosed techniques are applied inthe fabrication of each pixel color component of a current-resolutionhigh-definition television screen (e.g., pixels each having red, greenand blue wells, with pixels arranged in 1080 horizontal lines ofvertical resolution and 1920 vertical lines of horizontal resolution),there are approximately six million wells that might receive ink (i.e.,three overlapping arrays each of two million wells). Next generationtelevisions are expected to increase this resolution by a factor of fouror more. In such a process, to improve the speed of printing, printheads may use thousands of nozzles for printing, e.g., there willtypically be a staggering number of possible print process permutations.The simplified examples presented above are used to introduce conceptsbut it should be noted that, given the staggering numbers presented in atypical combination, permutations represented by a real-life televisionapplication are quite complex, with print optimization typically beingapplied by software and using complex mathematical operations. FIGS. 4-7are used to provide non-limiting examples of how these operations can beapplied.

Note that the techniques introduced in this disclosure can be manifestedin a number of different ways. For example, FIG. 4 represents a numberof different implementation tiers, collectively designated by referencenumeral 401; each one of these tiers represents a possible discreteimplementation of the techniques introduced above. First, the techniquesintroduced above can be embodied as instructions stored onnon-transitory machine-readable media, as represented by graphic 403(e.g., software for controlling a computer or a printer). Second, percomputer icon 405, these techniques can be implemented as part of acomputer or network, for example, within a company that designs ormanufactures components for sale or use in other products. For example,the techniques introduced above can be implemented as design software bya company that consults to, or performs design for, a high definitiontelevision (HDTV) manufacturer; alternatively, these techniques could beused directly by such a manufacturer to make televisions (or displayscreens). Third, as introduced earlier and exemplified using a storagemedia graphic 407, the techniques introduced earlier can take the formof printer instruction, e.g., as stored instructions or data that, whenacted upon, will cause a printer to fabricate one or more layers of acomponent dependent on the use of planned droplet aggregationtechniques, per the discussion above. Fourth, as represented by afabrication device icon 409, the techniques introduced above can beimplemented as part of a fabrication apparatus or machine, or in theform of a printer within such an apparatus or machine. For example, afabrication machine could be sold or customized in a manner wheredroplet measurement, and conversion of externally-supplied “layer data”is automatically converted by the machine (e.g., through the use ofsoftware) into printer instructions that will print using the techniquesdescribed here to transparently optimize/speed-up the printing process.Such data can also be computed off-line, and then reapplied on areproducible basis in a scalable, pipelined manufacturing process thatmanufactures many units. It is noted that the particular depiction ofthe fabrication device icon 409 represents one exemplary printer devicethat will be discussed below (e.g., in reference to FIGS. 8-9). Thetechniques introduced above can also be embodied as an assembly such asan array 411 of multiple components that will be separately sold; inFIG. 4 for example, several such components are depicted in the form ofan array of semi-finished flat panel devices, which will later beseparated and sold for incorporation into end consumer products. Thedepicted devices may have, for example, one or more layers (e.g., colorcomponent layers, semiconductor layers, encapsulation layers or othermaterials) deposited in dependence on the methods introduced above. Thetechniques introduced above can also be embodied in the form ofend-consumer products as referenced, e.g., in the form of displayscreens for portable digital devices 413 (e.g., such as electronic padsor smart phones), as television display screens 415 (e.g., HDTVs), orother types of devices. For example, FIG. 4 uses a solar panel graphic417 to denote that the processes introduced above can be applied toother forms of electronic devices, e.g., to deposit per-target regionstructures (such as one or more layers of individual cells that make upan aggregate device) or blanket layers (e.g., an encapsulation layer fora TV or solar panel). Clearly, many examples are possible.

The techniques introduced above, without limitation, can be applied toany of the tiers or components illustrated in FIG. 4. For example, oneembodiment of the techniques disclosed herein is an end consumer device;a second embodiment of the techniques disclosed herein is an apparatuscomprising data to control the fabrication of a layer using combinationsof specific nozzle volumes to obtain specific per-target region fills;nozzle volumes can be determined in advance, or measured and applied insitu. Yet another embodiment is a deposition machine, for example, thatuses a printer to print one or more inks using techniques introducedabove. These techniques can be implemented on one machine or more thanone machine, e.g., a network or series of machines where different stepsare applied at different machines. All such embodiments, and others, canindependently make use of techniques introduced by this disclosure.

An exemplary process for planning printing is introduced by FIG. 5. Thisprocess and associated methods and devices are generally referencedusing the numeral 501.

More specifically, the droplet volume for each nozzle (and for eachnozzle for each waveform if multiple drive waveforms are applied) isspecifically determined (503). Such measurement can be performed forexample using a variety of techniques, including without limitation anoptical-imaging or laser-imaging device built into a printer (or afactory-resident machine) that images droplets during flight (e.g.,during a calibration printing operation or a live printing operation)and that calculates volume with precision based on droplet shape,velocity, trajectory and/or other factors. Other techniques can also beused including printing ink and then using post-printing imaging orother techniques to calculate individual droplet volumes based onpattern recognition. Alternatively, identification can be based on datasupplied by a printer or print head manufacturer, for example, based onmeasurements taken at a factory well prior to the fabrication processand supplied with a machine (or on-line). In some applications, dropletvolume characteristics can change over time, for example, dependent onink viscosity or type, temperature, nozzle clogging or otherdegradation, or because of other factors; therefore, in one embodiment,droplet volume measurement can be dynamically performed in situ, forexample, upon power up (or at occurrence of other types of power cycleevents), with each new printing of a substrate, upon expiration of apredetermined time or on another calendared or uncalendared basis. Asdenoted by numeral 504, this data (measured or provided) is stored foruse in an optimization process.

In addition to per-nozzle (and optionally, per-drive-waveform) dropletvolume data, information (505) is also received concerning desired fillvolume for each target region. This data can be a single target fillvalue to be applied to all target regions, respective target fill valuesto be applied to individual target regions, rows of target regions orcolumns of target regions, or values broken down in some other manner.For example, as applied to fabricating a single “blanket” layer ofmaterial that is large relative to individual electronic devicestructures (such as transistors or pathways), such data could consist ofa single thickness to be applied to an entire layer (e.g., whichsoftware then converts to a desired ink fill volume per target regionbased upon predetermined conversion data specific to the pertinent ink);in such a case, the data could be translated to a common value for each“print cell” (which in this case might be equivalent to each targetregion or consist of multiple target regions). In another example, thedata could represent a specific value (e.g., 50.00 pL) for one or morewells, with range data either being provided or understood based oncontext. As should be understood from these examples, the desired fillcan be specified in many different forms including, without limitation,as thickness data or volume data. Additional filtering or processingcriteria can also optionally be provided to or performed by a receivingdevice; for example, as referenced earlier, random variation in fillvolumes could be injected by a receiving device into one or moreprovided thickness or volume parameters to render line effect invisibleto the human eye in a finished display. Such variation could beperformed in advance (and provided as respective, per-target regionfills that vary from region to region) or could be independently andtransparently derived from a recipient device (e.g., by a downstreamcomputer or printer).

Based on the target fill volumes for each region and individual dropletvolume measurements (i.e., per-print head nozzle and per nozzle drivewaveform), the process then optionally proceeds to calculatecombinations of various droplets that sum to a fill volume within thedesired tolerance range (i.e., per process block 506). As mentioned,this range can be provided with target fill data or can be “understood”based on context. In one embodiment, the range is understood to be ±onepercent of a provided fill value. In another embodiment, the range isunderstood to be ±one-half percent of a provided fill value. Clearly,many other possibilities exist for tolerance ranges, whether larger orsmaller than these exemplary ranges.

At this point, an example would help convey one possible method forcalculating sets of possible droplet combinations. Returning tosimplified examples described earlier, it should be assumed that thereare five nozzles, each having respective hypothetical droplet volumes of9.80 pL, 10.01 pL, 9.89 pL, 9.96 pL, and 10.03 pL, and that it isdesired to deposit a target volume of 50.00 pL, ±½ percent (49.75pL-50.25 pL) in five wells. This method begins by determining the numberof droplets that can be combined to reach but not exceed the tolerancerange and, for each nozzle, the minimum and maximum number of dropletsfrom that nozzle that can be used in any acceptable permutation. Forexample, in this hypothetical, no more than a single droplet from nozzle(1), two droplets from nozzle (3) and four droplets from nozzle (4)could be used in any combination, given the minimum and maximum dropletvolumes of the nozzles under consideration. This step limits the numberof combinations that need be considered. Armed with such constraints onset consideration, the method then considers combinations of therequired number of droplets (five in this example), taking each nozzlein turn. For example, the method first starts with nozzle (1) with anunderstanding that the only acceptable combinations involving thisnozzle feature one drop or fewer from this nozzle. Consideringcombinations involving a single droplet from this nozzle, the methodthen considers minimum and maximum drop volumes of the othernozzle-waveform combinations under consideration; for example, giventhat nozzle (1) is determined to produce a droplet volume of 9.80 pL fora given drive waveform, no more than one droplet from nozzle (3) or twodroplets from nozzle (4) can be used in combination with a droplet fromnozzle (1) to reach the desired tolerance range. The method proceeds toconsider combinations of the droplet from nozzle (1) and a combinationof four droplets from other nozzles, for example, four from nozzles (2)or (5), three droplets from nozzle (2) and one droplet from nozzle (4),and so on. Considering combinations involving nozzle (1) only, tosimplify discussion, any of the following different combinationsinvolving the first nozzle could potentially be used within thetolerance range:

{1(1),4(2)}, {1(1),3(2),1(4)}, {1(1),3(2),1(5)}, {1(1),2(2),1(4),1(5)},{1(1),1(2),1(3),2(5)}, {1(1),1(2),1(4),2(5)}, {1(1),1(2),3(5)},{1(1),1(3),3(5)}, {1(1),2(4),2(5)}, {1(1),1(4),3(5)} and {1(1),4(5)}.

In the mathematical expression set forth above, the use of bracketsdenotes a set of five droplets representing droplet volume combinationsfrom one or more nozzles, with each parenthetical within these bracketsidentifying the specific nozzle; for example, the expression {1(1),4(2)}represents one droplet from nozzle (1) and four droplets from nozzle(2), 9.80 pL+(4×10.01 pL)=49.84 pL, which is within the specifiedtolerance range. In effect, the method in this example considers thehighest number of droplets from the nozzle (1) that can be used toproduce the desired tolerance, evaluates combinations involving thishighest number, reduces the number by one, and repeats the process ofconsideration. In one embodiment, this process is repeated to determineall possible sets of non-redundant droplet combinations that can beused. When combinations involving nozzle (1) have been fully explored,the method proceeds to combinations involving nozzle (2) but not nozzle(1) and repeats the process, and so forth, testing each possible nozzlecombination to determine whether it can achieve the desired tolerancerange. In this embodiment for example, the method has determined thatcombinations of two or more droplets from nozzle (1) cannot be used, soit begins with consideration of combinations involving one droplet fromnozzle (1) and four droplets from other nozzles in various combination.The method in effect evaluates whether four droplets of nozzle (2) canbe used, determines that it can {1(1),4(2)}, then drops this number byone (three droplets from nozzle 2), and determines that this number canbe used in combination with a single droplet from nozzles (4) or (5),yielding acceptable sets of {1(1),3(2),1(4)}, {1(1),3(2),1(5)}. Themethod then further reduces the number of acceptable droplets fromnozzle (2) by one, and evaluates combinations of {1(1),2(2) . . . }, andthen {1(1),1(2) . . . }, and so forth. Once combinations involvingnozzle (2) have been considered in combination with a droplet fromnozzle (1), the method then takes the next nozzle, nozzle (3), andconsiders combinations of nozzle (1) involving this nozzle but notnozzle (2) and determines that the only acceptable combination is givenby {1(1),1(3),3(5)}. Once all combinations involving a droplet fromnozzle (1) have been considered, the method then considers 5-dropletcombinations involving droplets from nozzle (2) but not nozzle (1),e.g., {5(2)}, {4(2),1(3)}, {4(2),1(4)}, {4(2),1(5)}, {3(2),2(3)},{3(2),1(3),1(4)} and so on.

It is also noted that the same approach applies equally in the case thatthe nozzles can be driven by multiple firing waveforms (each generatingdifferent droplet volumes). These additional nozzle-waveformcombinations simply provide additional droplet volumes for use inselecting the set of droplet combinations that are within the targetvolume tolerance range. The use of multiple firing waveforms can alsoimprove the efficiency of the printing process by making available alarger number of acceptable droplet combinations and thereby increasingthe likelihood of concurrently firing droplets from a large fraction ofthe nozzles on each pass. In the case that nozzles have multiple drivingwaveforms and geometric steps are also used, the selection of a set ofdroplet combinations will incorporate both the geometric offset to beused in a given scan and the nozzle waveform that will be used for eachnozzle.

Note that, for purposes of narration, a brute force approach has beendescribed and that a staggering number of possible combinations willtypically be presented in practice, e.g., where the number of nozzlesand target regions are large (e.g., more than 128 each). However, suchcomputation is well within the capabilities of a high-speed processorhaving appropriate software. Also, note that there exist variousmathematical shortcuts that can be applied to reduce computation. Forexample, in a given embodiment, the method can exclude fromconsideration any combination that would correspond to use of less thanhalf of the available nozzles in any one pass (or alternatively, canlimit consideration to combinations that minimize volume variance acrosstarget regions (TR) in any single pass). In one embodiment, the methoddetermines only certain sets of droplet combinations that will produceacceptable aggregate fill values; in a second embodiment, the methodexhaustively calculates every possible set of droplet combinations thatwill produce acceptable aggregate fill values. It is also possible touse an iterative approach where, in multiple repetitions, a print scanis performed, and volumes of ink still remaining to be deposited toreach the desired tolerance range(s) are considered for purposes ofoptimizing a next, succeeding scan. Other processes are also possible.

Note also that as an initial operation, if the same fill value (andtolerance) applies to each target region, it suffices to compute thecombinations once (e.g. for one target region) and to store thesepossible droplet combinations for initial use with each target region.This is not necessarily the case for all set computation methods and forall applications (e.g., in some embodiments, the acceptable fill rangecan vary for every target region).

In yet another embodiment, the method uses mathematical shortcuts, suchas approximations, matrix math, random selection or other techniques, todetermine sets of acceptable droplet combinations for each targetregion.

As denoted by process block 507, once sets of acceptable combinationshave been determined for each target region, the method then effectivelyplans scanning in a way that correlates with a particular set (ordroplet combination) for each target region. This particular setselection is performed in a manner where the particular set (one foreach target region) represents process savings through the use of atleast one scan to deposit droplet volumes concurrently in multipletarget regions. That is to say, in an ideal case, the method selects oneparticular set for each target region, where the particular setrepresents particular droplet volume combinations in a manner where aprint head can simultaneously print into multiple rows of target regionsat once. The particular droplet choices in the selected combinationsrepresent a print process matching a predetermined criterion, such asminimal printing time, minimal number of scans, minimal sizes ofgeometric steps, minimal aggregate geometric step distance, or othercriteria. These criteria are represented by numeral 508 in FIG. 5. Inone embodiment, optimization is pareto optimal, with the particular setsselected in a manner that minimizes each of number of scans, aggregategeometric step distance and sizes of geometric steps, in that order.Again, this selection of particular sets can be performed in any desiredmanner, with several non-limiting examples further discussed below.

In one example, the method selects a droplet from each set for eachtarget region corresponding to a particular geometric step or waveformapplied to all regions being considered, and it then subtracts thisdroplet from available sets and determines a remainder. For example, ifchoices of available sets is initially {1(1),4(2)}, {1(1),3(2),1(4),{1(1),3(2),1(5)}, {1(1),2(2),1(4),1(5)}, {1(1),1(2),1(3),2(5)},{1(1),1(2),1(4),2(5)}, {1(1),1(2),3(5)}, {1(1),1(3),3(5)},{1(1),2(4),2(5)}, {1(1),1(4),3(5)} and {1(1),4(5)} for each of fivetarget regions, this embodiment would subtract one droplet (1) from thisinitial set to obtain a remainder specific to a first of the five targetregions, one droplet (2) from the initial set to obtain a remainderspecific to a second of the five target regions, one droplet (3) fromthe initial set to obtain a remainder specific to the third of thetarget regions, and so on. This evaluation would represent a geometricstep of “0.” The method would then evaluate the remainders and repeatthe process for other possible geometric steps. For example, if ageometric step of “−1” was then applied, the method would subtract onedroplet (2) from the initial set for the first of the five targetregions, one droplet (3) from the initial set from the second of thetarget regions and so forth, and evaluate the remainders.

In selecting a particular geometric step (and nozzle firing) as part ofprint planning, the method analyzes the various remainders according toa scoring or priority function, and selects the geometric step with thebest score. In one embodiment, scoring is applied to more heavily weighta step that (a) maximizes the number of nozzles used simultaneously and(b) maximizes the minimum number of combinations remaining for affectedtarget regions. For example, a scan that used droplets from four nozzlesduring a scan would be more heavily favored than one that used dropletsfrom just two nozzles. Similarly, if using the subtraction processdiscussed above in considering different steps resulted in 1, 2, 2, 4and 5 remaining combinations for respective target regions for onepossible step, and 2, 2, 2, 3 and 4 remaining combinations forrespective target regions for a second possible step, the method wouldmore heavily weight the latter (i.e., the largest minimum number is“2”). In practice, suitable weighting coefficients can be empiricallydeveloped. Clearly, other algorithms can be applied, and other forms ofanalysis or algorithmic shortcuts can be applied. For example, matrixmath can be used (e.g., using an eigenvector analysis) to determineparticular droplet combinations and associated scanning parameters thatsatisfy predetermined criteria. In another variation, other formulae canused, for example, that factor in use of planned random fill variationto mitigate line effect.

Once the particular sets and/or scan paths have been selected pernumeral 507, printer actions are sequenced, per numeral 509. Forexample, it is noted that a set of droplets can typically be depositedin arbitrary order if aggregate fill volumes were the onlyconsideration. If the printing is planned to minimize the number ofscans or passes, the order of geometric steps can also be selected tominimize print head/substrate motion; for example, if acceptable scansin a hypothetical example involve geometric steps of {0,+3, −2,+6 and−4}, these scans can be reordered to minimize print head/substratemotion and thus further improve printing speed, for example, orderingthe scans as a sequence of steps of {0,+1,+1,+2 and +4}. Compared to thefirst sequence of geometric steps {0,+3, −2,+6 and −4}, involving anaggregate step increment distance of 15, the second sequence ofgeometric steps {0,+1,+1,+2 and +4} involves an aggregate step incrementdistance of 8, facilitating faster printer response.

As denoted by numeral 510, for applications involving large numbers ofrows of target regions which are to receive the same target fill, aparticular solution can also be expressed as a repeatable pattern whichis then reproduced over subset areas of the substrate. For example, ifin one application there were 128 nozzles arranged in a single row and1024 rows of target regions, it is expected than an optimal scan patterncould be determined for a subset area of 255 rows of target regions orfewer; thus, the same print pattern could be applied to four or moresubset areas of the substrate in this example. Some embodimentstherefore take advantage of repeatable patterns as expressed by optionalprocess block 510.

Note the use of non-transitory machine-readable media icon 511; thisicon denotes that the method described above is optionally implementedas instructions for controlling one or more machines (e.g., software orfirmware for controlling one or more processors). The non-transitorymedia can include any machine-readable physical medium, for example, aflash drive, floppy disk, tape, server storage or mass storage, dynamicrandom access memory (DRAM), compact disk (CD) or other local or remotestorage. This storage can be embodied as part of a larger machine (e.g.,resident memory in a desktop computer or printer) or on an isolatedbasis (e.g., flash drive or standalone storage that will later transfera file to another computer or printer). Each function mentioned inreference to FIG. 5 can be implemented as part of a combined program oras a standalone module, either stored together on a single mediaexpression (e.g., single floppy disk) or on multiple, separate storagedevices.

As represented by numeral 513 in FIG. 5, once the planning process iscompleted, data will have been generated that effectively represent aset of printer instructions, comprising nozzle firing data for the printhead and instructions for relative movement between print head andsubstrate to support the firing pattern. This data, effectivelyrepresenting the scan path, scan order and other data, is an electronicfile (513) that can either be stored for later use (e.g., as depicted bynon-transitory machine-readable media icon 515), or immediately appliedto control a printer (517) to deposit ink representing the selectedcombinations (particular sets of nozzles per target region). Forexample, the method can be applied on a standalone computer, with theinstruction data being stored in RAM for later use, or for download toanother machine. Alternatively, the method could be implemented anddynamically applied by a printer to “inbound” data, to automaticallyplan scanning dependent on printer parameters (such asnozzle-droplet-volume data). Many other alternatives are possible.

FIGS. 6A-6C provide flowcharts that generally relate to the nozzleselection and scan planning process. Note again that scans do not haveto be continuous or linear in direction or speed of movement and do nothave to proceed all the way from one side of a substrate to another.

A first block diagram is denoted by numeral 601 in FIG. 6A; this FIG.represents many of the exemplary processes discussed in the previousnarration. The method first begins by retrieving from memory sets ofacceptable droplet volume combinations for each target region, pernumeral 603. These sets can be dynamically computed or could have beencomputed in advance, for example, using software on a different machine.Note the use of a database icon, 605, representing either a local-storeddatabase (for example, stored in local RAM) or a remote database. Themethod then effectively selects a particular one of the acceptable setsfor each target region (607). This selection in many embodiments isindirect, that is, the method processes the acceptable combinations toselect particular scans (for example, using the techniques referencedabove), and it is these scans that in effect define the particular sets.Nevertheless, by planning scanning, the method selects particular setsof combinations for each respective target region. This data is thenused to order scans and finalize motion and firing patterns (609) asreferenced above.

The middle and right of FIG. 6A illustrate a few process options forplanning scan paths and nozzle firing patterns and, in effect, selectinga particular droplet combination for each target region in a manner thatrepresents printing optimization. As denoted by numeral 608, theillustrated techniques represent but one possible methodology forperforming this task. Per numeral 611, analysis can involve determiningminimum and maximum use of each nozzle (or nozzle-waveform combination,in those instances in which a nozzle is driven by more than one firingwaveform) in acceptable combinations. If a particular nozzle is bad(e.g., does not fire, or fires at an unacceptable trajectory), thatnozzle can be ruled out for use (and for consideration). Second, if anozzle has either a very small or very large droplet volume, this maylimit the number of droplets that can be used from that nozzle inacceptable combinations; numeral 611 represents advance processing thatreduces the number of combinations that will be considered. Asrepresented by numeral 612, processes/shortcuts can be used to limit thenumber of sets of droplet combinations that will be evaluated; forexample, instead of considering “all” possible droplet combinations foreach nozzle, the method can be configured to optionally rule outcombinations involving fewer than half of the nozzles (or anotherquantity of the nozzles, such as ¼), combinations where more thanone-half of the droplets come from any particular nozzle-waveform, orcombinations representing a high variance in droplet volume orrepresenting a large variance in simultaneous droplet volumes appliedacross target regions. Other metrics can also be used.

Subject to any limitations to the number of sets to becomputed/considered, the method then proceeds to calculate and consideracceptable droplet combinations, per numeral 613. As referenced bynumerals 614 and 615, various processes can be used to plan scanningand/or otherwise effectively select a particular set of droplet volumesper target region (TR). For example, as introduced above, one methodassumes a scan path (e.g., particular geometric step selection) and thenconsiders the maximum of the fewest remaining set choices across all TRsbeing considered; the method can favorably weight those scan paths(alternative geometric steps) that maximize ability of ensuing scans tocover multiple target regions at-once. Alternatively or in addition, themethod can favorably weight geometric steps that maximize the number ofnozzles used at once; returning to the simplified five-nozzle discussionabove, a scan that would apply five nozzles to a target region can beweighted more favorably that a scan or pass that would fire only threenozzles in a pass. Thus, in one embodiment, the following algorithm canbe applied by software:

S _(i) =[w ₁ f{max{#RemCombs_(TR,i) }+w ₂ f{max{#Simult.Nozzles_(i)}].

In this exemplary equation, “i” represents the particular choice ofgeometric step or scan path, w₁ represents one empirically-determinedweighting, w₂ represents a second empirically-determined weighting,#RemCombs_(TR,i) represents the number of remaining combinations pertarget region assuming scan path i, and #Simult.Nozzles_(i) represents ameasure of the number of nozzles used for scan path i; note that thislatter value need not be an integer, e.g., if fill values per TR arevaried (for example, to hide potentially visible artifacts in a displaydevice), a given scan path could feature varying numbers of nozzles usedper column of target region, e.g., an average or some other measure canbe used. Note also that these factors and the weightings areillustrative only, i.e., it is possible to use different weightingand/or considerations than these, use only one variable but not theother, or to use a completely different algorithm.

FIG. 6A also shows a number of further options. For example,consideration of droplet sets in one implementation is performedaccording to an equation/algorithm, per numeral 617. A comparativemetric can be expressed as a score that can be calculated for eachpossible alternative geometric step in order to select a particular stepor offset. For example, another possible algorithmic approach involvesan equation with three terms, as shown below:

S _(i) =W _(v)(S _(v,min) /S _(v))+W _(e)(S _(e) /S _(e,max))+W _(d)(S_(d,min) /S _(d)),

where the terms based on S_(v), S_(e) and S_(d) are scores respectivelycomputed for variance in deposited droplet volumes, efficiency (maximumnozzles used per-pass) and variation in geometric step. In oneformulation, the term “(S_(v,min)/S_(v))” seeks to minimize variation infill volume from a per-pass target value in a manner dependent on thetotal number of droplets.

Numeral 619 in FIG. 6A represents that, in one embodiment, dropletcombination selection can be performed using matrix math, for example,through the use of mathematical techniques that simultaneously considerall droplet volume combinations and that use a form of eigenvectoranalysis to select scan paths.

As represented by numeral 621, an iterative process can be applied toreduce the number of considered droplet combinations. That is, forexample, as represented by the earlier narration of one possibleprocessing technique, geometric steps can be computed one at a time.Each time a particular scan path is planned, the method determines theincremental volume still needed in each target region underconsideration, and then proceeds to determine a scan or geometric offsetbest suited to producing aggregate volumes or fill volumes per targetregion that are within desired tolerances. This process can then berepeated as respective iterations until all scan paths and nozzle firingpatterns have been planned.

Per numeral 622, use of a hybrid process is also possible. For example,in one embodiment, a first set of one or more scans or geometric stepscan be selected and used, for example, based on minimized deviation inper-nozzle droplet volume and maximum efficiency (e.g., nozzles used perscan). Once a certain number of scans have been applied, e.g., 1, 2, 3or more, a different algorithm can be invoked, for example, thatmaximizes nozzles used per scan (e.g., irrespective of deviation inapplied droplet volumes). Any of the specific equations or techniquesdiscussed above (or other techniques) can optionally be applied one ofthe algorithms in such a hybrid process, and other variations will nodoubt occur to those skilled in the art.

Note that as referenced earlier, in an exemplary display-manufacturingprocess, per-target region fill volumes can have planned randomizationdeliberately injected (623) to mitigate line effect. In one embodiment,a generator function (625) is optionally applied to deliberately varytarget fill volumes (or to skew aggregate volumes produced for thedroplet combination for each target region) in a manner that achievesthis planned randomization or other effect. As noted earlier, in adifferent embodiment, it is also possible for such variation to befactored into target fill volumes and tolerances, i.e., before dropletcombinations are even analyzed, and to apply, for example, algorithmicapproaches as indicated earlier to meet per-target-region fillrequirements.

FIG. 6B and numeral 631 refer to a more detailed block diagram relatedto the iterative solution referenced above. As represented by numerals633 and 635, possible droplet combinations are once again firstidentified, stored, and retrieved as appropriate, for evaluation bysoftware. For each possible scan path (or geometric step), per numeral637, the method stores a footprint identifying the scan path (639) andnozzles applied, and it subtracts per nozzle firings from the per-targetregion sets (641) to determine remainder combinations for each targetregion (643). These are also stored. Then, per numeral 645, the methodevaluates the stored data according to predefined criteria. For example,as indicated by optional (dashed-line) block 647, a method that seeks tomaximize the minimum number of droplet combinations across all pertinenttarget regions can assign a score indicating whether the just-storedcombination is better than, or worse than, previously consideredalternatives. If the specified criteria are met (645), the particularscan or geometric step can be selected, with the remainder combinationsbeing stored or otherwise flagged for use in consideration of anotherprint head/substrate scan or pass, as represented by numerals 649 and651. If the criteria are not met (or consideration is incomplete),another step can be considered and/or the method can adjustconsideration of the geometric step under consideration (or a previouslyselected step), per numeral 653. Again, many variations are possible.

It was noted earlier that the order in which scans are performed ordroplets are deposited is unimportant to ultimate fill values for thetarget region. While this is true, to maximize printing speed andthroughput, scans are preferably ordered so as to result in the fastestor most efficient printing possible. Thus, if not previously factoredinto geometric step analysis, the sorting and/or ordering of scans orsteps can then be performed. This process is represented by FIG. 6C.

In particular, numeral 661 is used to generally designate the method ofFIG. 6C. Software, for example, running on a suitable machine, causes aprocessor to retrieve (663) the selected geometric steps, particularsets, or other data that identifies the selected scan paths (and asappropriate, nozzle firing patterns, which can further include dataspecifying which of a plurality of firing waveforms is to be used foreach droplet, in those embodiments in which certain nozzles can bedriven by more than one firing waveforms). These steps or scans are thensorted or ordered in a manner that minimizes incremental step distance.For example, again referring to the hypothetical example introducedearlier, if the selected steps/scan paths were {0,+3, −2,+6 and −4},these might be reordered greatest to minimize each incremental step andto minimize overall (aggregate) distance traversed by a motion system inbetween scans. Without reordering for example, the incremental distancesbetween these offsets would be equivalent to 3, 2, 6 and 4 (such thatthe aggregate distances traversed would be “15” in this example). If thescans (e.g., scans “a,” “b,” “c,” “d” and “e”) were reordered in themanner described (e.g., in order of “a,” “c,” “b,” “e” and “d”), theincremental distances would be +1,+1, +2 and +4 (such that the aggregatedistances traversed would be “8”). As denoted by numeral 667, at thispoint, the method can assign motion to a print head motion system and/ora substrate motion system, and can reverse the order of nozzle firing(e.g., if alternating, reciprocal scan path directions are used, pernumerals 219 and 220 of FIG. 2A). As noted earlier and represented byoptional process block 669, in some embodiments, planning and/oroptimization can be performed for a subset of the target regions, with asolution then applied on a spatially-repeating basis over a largesubstrate.

This repetition is represented in part by FIG. 6D. As implied by FIG.6D, it should be assumed for this narration that it is desired tofabricate an array of flat panel devices. A common substrate isrepresented by numeral 681, and a set of dashed-line boxes, such as box683, represents geometry for each flat panel device. A fiducial 685,preferably with two-dimensional characteristics, is formed on thesubstrate and used to locate and align the various fabricationprocesses. Following eventual completion of these processes, each panel683 will be separated from the common substrate using a cutting orsimilar process. Where the arrays of panels represent respective OLEDdisplays, the common substrate 681 will typically be glass, withstructures deposited atop the glass, followed by one or moreencapsulation layers; each panel will then be inverted such that theglass substrate forms the light emitting surface of the display. Forsome applications, other substrate materials can be used, for example, aflexible material, transparent or opaque. As noted, many other types ofdevices can be manufactured according to the described techniques. Asolution can be computed for a specific subset 687 of a flat panel 683.This solution can then be repeated for other, similarly-sized subsets689 of the flat panel 683, and the entire solution set can then also berepeated for each panel to be formed from a given substrate.

Reflecting on the various techniques and considerations introducedabove, a manufacturing process can be performed to mass produce productsquickly and at low per-unit cost. Applied to display device manufacture,e.g., flat panel displays, these techniques enable fast, per-panelprinting processes, with multiple panels produced from a commonsubstrate. By providing for fast, repeatable printing techniques (e.g.,using common inks and print heads from panel-to-panel), it is believedthat printing can be substantially improved, for example, reducingper-layer printing time to a small fraction of the time that would berequired without the techniques above, all while guaranteeing per-targetregion fill volumes are within specification. Again returning to theexample of large HD television displays, it is believed that each colorcomponent layer can be accurately and reliably printed for largesubstrates (e.g., generation 8.5 substrates, which are approximately 220cm×250 cm) in one hundred and eighty seconds or less, or even ninetyseconds or less, representing substantial process improvement. Improvingthe efficiency and quality of printing paves the way for significantreductions in cost of producing large HD television displays, and thuslower end-consumer cost. As noted earlier, while display manufacture(and OLED manufacture in particular) is one application of thetechniques introduced herein, these techniques can be applied to a widevariety of processes, computer, printers, software, manufacturingequipment and end-devices, and are not limited to display panels.

One benefit of the ability to deposit precise target region volumes(e.g., well volumes) within tolerance is the ability to injectdeliberate variation within tolerance, as mentioned. These techniquesfacilitate substantial quality improvements in displays, because theyprovide the ability to hide pixelated artifacts of the display,rendering such “line effect” imperceptible to the human eye. FIG. 7provides a block diagram 701, associated with one method for injectingthis variation. As with the various methods and block diagrams discussedabove, the block diagram 701 and related method can optionally beimplemented as software, either on standalone media, or as part of alarger machine.

As denoted by numeral 703, variation can be made to depend on specificfrequency criteria. For example, it is generally understood thatsensitivity of the human eye to contrast variation is a function ofbrightness, expected viewing distance, display resolution, color andother factors. As part of the frequency criteria, a measure is used toensure that, given typical human-eye sensitivity to spatial variation incontrast between colors at different brightness levels, such variationwill be smoothed in a manner not perceptible to the human eye, e.g.,varied in a manner that does not contribute human-observable patterns in(a) any direction or directions, or (b) between color components givenexpected viewing conditions. This can be achieved optionally using aplanned randomization function, as referenced earlier. With minimumcriteria specified, the target fill volumes for each color component andeach pixel can be deliberately varied in a manner calculated to hide anyvisible artifacts from the human eye, as represented by numeral 705.Note that the right side of FIG. 7 represents various process options,for example, that variation can be made independent across colorcomponents (707), with tests for perceptible patterns applied on analgorithmic basis to ensure that fill variations do not give rise toperceptible patterns. As noted by numeral 707, for any given colorcomponent (e.g., any given ink), variation can also be made independentin each of multiple spatial dimensions, for example, x and y dimensions(709). Again, in one embodiment, not only is the variation smoothed foreach dimension/color component so as to not be perceptible, but anypattern of differences between each of these dimensions is alsosuppressed so as to not be visible. Per numeral 711, a generatorfunction or functions can be applied to ensure that these criteria aremet, for example, by optionally assigning minor target fill variationsto each target region's fill prior to droplet volume analysis, using anydesired criteria. As denoted by numeral 713, in one embodiment, thevariation can optionally be made to be random.

Per numeral 715, selection of the particular droplet combinations foreach target region are thus weighted in favor of the selected variationcriteria. This can be performed, as mentioned, via target fillvariation, or at the time of droplet (e.g., scan path, nozzle-waveformcombination, or both) selection. Other methods for imparting thisvariation also exist. For example, in one contemplated implementation,per numeral 717, the scan path is varied in a nonlinear manner,effectively varying droplet volumes across mean scan path direction. Pernumeral 719, nozzle firing patterns can also be varied, for example byadjusting firing pulse rise time, fall time, voltage, pulse width orusing multiple signal levels per pulse (or other forms of pulse shapingtechniques) to provide minor droplet volume variations; in oneembodiment, these variations can be calculated in advance, and in adifferent embodiment, only waveform variations that create very minorvolume variations are used, with other measures employed to ensure thataggregate fills stay within specified tolerance ranges. In oneembodiment, for each target region, a plurality of droplet combinationsthat fall within specified tolerance ranges are computed and for eachtarget region, the selection of which droplet combination is used inthat target region is varied (e.g. randomly or based on a mathematicalfunction), thereby effectively varying the droplet volumes across thetarget regions and mitigating line effects. Such variation can beimplemented along the scan path direction over a row of target regions,over a column of target regions, or over both.

FIGS. 8A-9C are used to provide simulation data for techniques discussedhere. FIGS. 8A-8C represent fill volumes based on five droplets, whereasFIGS. 9A-9C represent fill volumes based on ten droplets. For each ofthese figures, the letter designation “A” (e.g., FIGS. 8A and 9A)represents a situation where nozzles are used to deposit dropletswithout consideration as to volume differences. By contrast, the letterdesignation “B” (e.g., FIGS. 8B and 9B) represents situations where arandom combination of (5 or 10) droplets are selected to “average out”expected volume differences between nozzles. Finally, the letterdesignation “C” (e.g., FIGS. 8C and 9C) represents situations wherescans and nozzle firings are dependent on specific aggregate ink volumesper target region that seek to minimize aggregate fill variance acrosstarget regions. In these various FIGS., the variation per nozzle isassumed to be consistent with variation observed in actual devices, eachvertical axis represents aggregate fill volumes in pL, and eachhorizontal axis represents the number of target regions, for example,pixel wells or pixel color components. Note that the emphasis of theseFIGS. is to show variation in aggregate fill volumes, assuming randomlydistributed droplet variations about an assumed average. For FIGS.8A-8C, the average volume is per nozzle is assumed to be slightly below10.00 pL per nozzle, and for FIGS. 9A-9C, the average droplet volume pernozzle is assumed to be slightly above 10.00 pL per nozzle.

A first graph 801 represented in FIG. 8A shows per-well volumevariations assuming differences in nozzle droplet volumes with noattempt to mitigate these differences. Note that these variations can beextreme (e.g., per peak 803), with a range of aggregate fill volumes ofabout ±2.61%. As mentioned, the average of five droplets is slightlybelow 50.00 pL; FIG. 8A shows two sets of sample tolerance rangescentered about this average, including a first range 805 representing arange of ±1.00% centered about this value, and a second range 807representing a range of ±0.50% centered about this value. As is seen bythe numerous peaks and troughs that exceed either range (e.g., peak803), such a printing process results in numerous wells that would failto meet specification (e.g., either one or the other of these ranges).

A second graph 811 represented in FIG. 8B shows per-well volumevariations using a randomized set of five nozzles per well, in an effortto statistically average out the effects of droplet volume variation.Note that such a technique does not permit precise production of aspecific volume of ink in any particular well, nor does such a processguarantee aggregate volumes within range. For example, although thepercentage of fill volumes falling outside of specification represents amuch better case than represented by FIG. 8A, there are still situationswhere individual wells (such as identified by trough 813) fall outsideof specification, for example the ±1.00% and ±0.50% variationrepresented by numerals 805 and 807, respectively. In such a case, themin/max error is ±1.01%, reflecting the improvement with random mixingrelative to the data presented in FIG. 8A.

FIG. 8C represents a third case, using specific combinations ofper-nozzle droplets according to techniques above. In particular, agraph 821 shows that variation is entirely within a ±1.00% range andquite close to meeting a ±0.50% range for all represented targetregions; once again, these ranges are represented by numerals 805 and807, respectively. In this example, five specifically elected dropletvolumes are used to fill the wells in each scan line, with the printhead/substrate shifts as appropriate for each pass or scan. The min/maxerror is ±0.595%, reflecting further improvement with this form of“smart mixing.” Note that the improvements and data observations will beconsistent for any form of intelligent, droplet volume combinations toachieve specific fills or tolerance ranges, e.g., where offsets betweennozzle rows (or multiple print heads) are used, or where multiplepreselected drive waveforms are used to permit combination ofspecifically selected droplet volumes.

As mentioned, FIGS. 9A-9C present similar data, but assumingcombinations of 10 droplets per well, with an average droplet volume ofabout 10.30 pL per nozzle. In particular, graph 901 in FIG. 9Arepresents a case where no attention is given to mitigating dropletvolume differences, graph 911 in FIG. 9B represents a case wheredroplets are applied randomly in an effort to statistically “averageout” volume differences, and graph 921 in FIG. 9C represents a case ofplanned mixing of specific droplets (to achieve the average fill volumesof FIGS. 9A/9B, i.e., approximately 103.10 pL). These various FIGS. showtolerance ranges of ±1.00% and ±0.50% variation about this average,respectively denoted using range arrows 905 and 907. Each of the FIGS.further shows respective peaks 903, 913 and 923 represented byvariation. Note however, that FIG. 9A represents a variation of ±2.27%about target, FIG. 9B represents a variation of ±0.707% about target andFIG. 9C represents a variation of ±0.447% about target. With theaveraging of a larger number of droplets, the “random droplet” solutionof FIG. 9B is seen to achieve a ±1.00% tolerance range about the averagebut not a ±0.50% range. By contrast, the solution depicted by FIG. 9C isseen to meet both tolerance ranges, demonstrating that variation can beconstrained to lie within specification while still permitting variationin droplet combinations from well-to-well.

One optional embodiment of the techniques described in this disclosureis described in exactly these terms. That is, for a printing processwhere nozzles having a maximum droplet volume variation of x % are usedto deposit aggregate fill volumes having a maximum expected volumevariation of y %, conventionally, there exist few means of guaranteeingthat aggregate fill volumes will vary by less than x %. For applicationswhere x % is greater than y %, this presents a potential problem. Adroplet averaging technique (e.g., as represented by the data seen inFIGS. 8B and 9B) statistically reduces volume variation across targetregions to an expected variance of x %/(n)^(1/2), where n is the averagenumber of droplets needed per target region to achieve desired fillvolumes. Note that even with such a statistical approach, there is nomechanism for reliably ensuring that actual target region fill volumeswill sit within a tolerance of y %. The techniques discussed hereinprovide a mechanism for providing such reliability. One optionalembodiment therefore provides a method of generating control data, orcontrolling a printer, and related apparatuses, systems, software andimprovements where statistical volume variance across target regions isbetter than x %/(n)^(1/2) (e.g., substantially better than x%/(n)^(1/2)). In a specific implementation, this condition is met undercircumstances where print head nozzles are concurrently used to depositdroplets in respective rows of target regions (e.g., respective pixelwell) with each scan. Perhaps otherwise stated, in such a specificimplementation, nozzles representing a droplet variation of ±x % of atarget droplet volume have their droplets combined to achieve targetregion fill volumes where target region aggregate fill volumes have astatistical variance of less than x %/(n)^(1/2) and feature concurrentuse of different nozzles for different, respective rows of targetregions for each print head/substrate scan.

With a set of basic techniques for combining droplets such that the sumof their volumes is specifically chosen to meet specific targets thusdescribed, this document will now turn to a more detailed discussion ofspecific devices and applications that can benefit from theseprinciples. This discussion is intended to be non-limiting, i.e., todescribe a handful of specifically contemplated implementations forpracticing the methods introduced above.

As seen in FIG. 10, a multi-chambered fabrication apparatus 1001includes several general modules or subsystems including a transfermodule 1003, a printing module 1005 and a processing module 1007. Eachmodule maintains a controlled environment, such that printing forexample can be performed by the printing module 1005 in a firstcontrolled atmosphere and other processing, for example, anotherdeposition process such an inorganic encapsulation layer deposition or acuring process (e.g., for printed materials), can be performed in asecond controlled atmosphere. The apparatus 1001 uses one or moremechanical handlers to move a substrate between modules without exposingthe substrate to an uncontrolled atmosphere. Within any given module, itis possible to use other substrate handling systems and/or specificdevices and control systems adapted to the processing to be performedfor that module.

Various embodiments of the transfer module 1003 can include an inputloadlock 1009 (i.e., a chamber that provides buffering between differentenvironments while maintaining a controlled atmosphere), a transferchamber 1011 (also having a handler for transporting a substrate), andan atmospheric buffer chamber 1013. Within the printing module 1005, itis possible to use other substrate handling mechanisms such as aflotation table for stable support of a substrate during a printingprocess. Additionally, an xyz-motion system, such as a split axis organtry motion system, can be used for precise positioning of at leastone print head relative to the substrate, as well as providing a y-axisconveyance system for the transport of the substrate through theprinting module 1005. It is also possible within the printing chamber touse multiple inks for printing, e.g., using respective print headassemblies such that, for example, two different types of depositionprocesses can be performed within the printing module in a controlledatmosphere. The printing module 1005 can comprise a gas enclosure 1015housing an inkjet printing system, with means for introducing an inertatmosphere (e.g., nitrogen, a noble gas, another similar gas, or acombination thereof) and otherwise controlling the atmosphere forenvironmental regulation (e.g., temperature and pressure), gasconstituency and particulate presence.

A processing module 1007 can include, for example, a transfer chamber1016; this transfer chamber also has a handler for transporting asubstrate. In addition, the processing module can also include an outputloadlock 1017, a nitrogen stack buffer 1019, and a curing chamber 1021.In some applications, the curing chamber can be used to cure a monomerfilm into a uniform polymer film, for example, using a heat or UVradiation cure process.

In one application, the apparatus 1001 is adapted for bulk production ofliquid crystal display screens or OLED display screens in bulk, forexample, the fabrication of an array of eight screens at once on asingle large substrate. These screens can be used for televisions and asdisplay screens for other forms of electronic devices. In a secondapplication, the apparatus can be used for bulk production of solarpanels in much the same manner.

Applied to the droplet-volume combination techniques described above,the printing module 1005 can advantageously be used in display panelmanufacture to deposit one or more layers, such as light filteringlayers, light emissive layers, barrier layers, conductive layers,organic or inorganic layers, encapsulation layers and other types ofmaterials. For example, the depicted apparatus 1001 can be loaded with asubstrate and can be controlled to move the substrate back and forthbetween the various chambers to deposit and/or cure or harden one ormore printed layers, all in a manner uninterrupted by interveningexposure to an uncontrolled atmosphere. The substrate can be loaded viathe input loadlock 1009. A handler positioned in the transfer module1003 can move the substrate from the input loadlock 1009 to the printingmodule 1005, and following completion of a printing process, moved tothe processing module 1007 for cure. By repeated deposition ofsubsequent layers, each of controlled volume per target region,aggregate layer properties can be built up to suit any desiredapplication. Note once again that the techniques described above are notlimited to display panel manufacturing processes, and that manydifferent types of tools can be used. For example, the configuration ofthe apparatus 1001 can be varied to place the various modules 1003, 1005and 1007 in different juxtaposition; also, additional modules or fewermodules can also be used.

While FIG. 10 provides one example of a set of linked chambers orfabrication components, clearly many other possibilities exist. The inkdroplet deposition techniques introduced above can be used with thedevice depicted in FIG. 10, or indeed, to control a fabrication processperformed by any other type of deposition equipment.

FIG. 11 provides a block diagram showing various subsystems of oneapparatus that can be used to fabricate devices having one or morelayers as specified herein. Coordination over the various subsystems isprovided by a processor 1103, acting under instructions provided bysoftware (not shown in FIG. 11). During a fabrication process, theprocessor feeds data to a print head 1105 to cause the print head toeject various volumes of ink depending on firing instructions providedby, e.g., a halftone print image. The print head 1105 typically hasmultiple ink jet nozzles, arranged in a row (or rows of an array), andassociated reservoirs that permit jetting of ink responsive toactivation of a piezoelectric or other transducer per nozzle; such atransducer causes a nozzle to eject a controlled amount of ink in anamount governed by an electronic nozzle drive waveform signal applied tothe corresponding piezoelectric transducer. Other firing mechanisms canalso be used. The print head applies the ink to a substrate 1107 atvarious x-y positions corresponding to the grid coordinates withinvarious print cells, as represented by the halftone print image.Variation in position is effected both by a print head motion system1109 and substrate handling system 1111 (e.g., that cause the printingto describe one or more swaths across the substrate). In one embodiment,the print head motion system 1109 moves the print head back-and-forthalong a traveler, while the substrate handling system provides stablesubstrate support and “y” dimension transport of the substrate to enable“split-axis” printing of any portion of the substrate; the substratehandling system provides relatively fast y-dimension transport, whilethe print head motion system 1009 provides relatively slow x-dimensiontransport. In another embodiment, the substrate handling system 1111 canprovide both x- and y-dimension transport. In yet another embodiment,primary transport can be provided entirely by the substrate handlingsystem 1111. An image capture device 1113 can be used to locate anyfiducials and assist with alignment and/or error detection.

The apparatus also comprises an ink delivery system 1115 and a printhead maintenance system 1117 to assist with the printing operation. Theprint head can be periodically calibrated or subjected to a maintenanceprocess; to this end, during a maintenance sequence, the print headmaintenance system 1117 is used to perform appropriate priming, purge ofink or gas, testing and calibration, and other operations, asappropriate to the particular process.

As was introduced previously, the printing process can be performed in acontrolled environment, that is, in a manner that presents a reducedrisk of contaminants that might degrade effectiveness of a depositedlayer. To this effect, the apparatus includes a chamber controlsubsystem 1119 that controls atmosphere within the chamber, as denotedby function block 1121. Optional process variations, as mentioned, caninclude performing jetting of deposition material in presence of anambient nitrogen gas atmosphere.

As previously mentioned, in embodiments disclosed herein, individualdroplet volumes are combined to achieve specific fill volumes per targetregion, selected in dependence on a target fill volume. A specific fillvolume can be planned for each target region, with fill value varyingabout a target value within an acceptable tolerance range. For suchembodiments, droplet volumes are specifically measured, in a mannerdependent on ink, nozzle, drive waveform, and other factors. To thisend, reference numeral 1123 denotes an optional droplet volumemeasurement system, where droplet volumes 1125 are measured for eachnozzle and for each drive waveform and are then stored in memory 1127.Such a droplet measurement system, as mentioned earlier, can be anoptical strobe camera or laser scanning device (or other volumemeasurement tool) incorporated into a commercial printing device. In oneembodiment, such a device operates in real-time (or near real time) tomeasure individual droplet volumes, deposition trajectory, dropletvelocity, and similar data. This data is provided to processor 1103either during printing, or during a one-time, intermittent or periodiccalibration operation. As indicated by numeral 1129, a prearranged setof firing waveforms can also optionally be associated with each nozzle,for later use in producing specific per-target region dropletcombinations; if such a set of waveforms is used for the embodiment,droplet volume measurements are advantageously computed duringcalibration using the droplet measurement system 1127 for each nozzle,for each waveform. Providing a real-time or near-real-time dropletvolume measurement system greatly enhances reliability in providingtarget region volume fills within the desired tolerance range, asmeasurements can be taken as needed and processed (e.g., averaged) tominimize statistical volume measurement error.

Numeral 1131 refers to the use of print optimization software running onprocessor 1103. More specifically, this software, based on dropletvolumes 1125 (measured in situ or otherwise provided), uses thisinformation to plan printing in a way that combines droplet volumes asappropriate to obtain per target region specific fill volumes. In oneembodiment, per the examples above, the aggregate volume can be planneddown to the resolution of 0.01 pL or better, within a certain errortolerance. Once printing has been planned, the processor calculatesprinting parameters such as number and sequence of scans, droplet sizes,relative droplet firing times, and similar information, and builds aprint image used to determine nozzle firing for each scan. In oneembodiment, the print image is a halftone image. In another embodiment,a print head has multiple nozzles, as many as 10,000. As will bedescribed below, each droplet can be described according to a time valueand a firing value (e.g., data describing a firing waveform or dataindicating whether a droplet will be “digitally” fired). In anembodiment where geometric steps and binary nozzle firing decisions arerelied upon to vary droplet volumes per well, each droplet can bedefined by a bit of data, a step value (or scan number) and a positionalvalue indicating where the droplet is to be placed. In an implementationwhere scans represent continuous motion, a time value can be used as theequivalent of a positional value. Whether rooted in time/distance orabsolute position, the value describes a position relative to areference (e.g., a synchronization mark, position or pulse) thatspecifies with precision where and when a nozzle should be fired. Insome embodiments, multiple values can be used. For example, in onespecifically contemplated embodiment, a sync pulse is generated for eachnozzle in a manner that corresponds to each micron of relative printhead/substrate motion during a scan; relative to each sync pulse, eachnozzle is programmed with (a) an offset value describing an integerclock cycle delay before the nozzle is fired, (b) a 4-bit waveformselection signal, to describe one of fifteen waveform selectionspreprogrammed into memory dedicated to the particular nozzle driver(i.e., with one of the sixteen possible values specifying an “off” ornon-firing state of the nozzle), and (c) a repeatability valuespecifying whether the nozzle should be fired once only, once for everysync pulse or once for every n sync pulses. In such a case, the waveformselection and an address for each nozzle are associated by the processor1103 with specific droplet volume data stored in memory 1127, withfiring of a specific waveform from a specific nozzle representing aplanned decision that a specific, corresponding droplet volume is to beused to supply aggregate ink to a specific target region of thesubstrate.

FIGS. 12A-14C will be used to introduce other techniques that can beused to combine different droplet volumes to obtain precisionwithin-tolerance fill volumes for each target region. In a firsttechnique, rows of nozzles can be selectively offset relative to oneanother during printing (e.g., in between scans). This technique isintroduced with reference to FIGS. 12A-12B. In a second technique,nozzle drive waveforms can be used to adjust piezoelectric transducerfiring and thus properties of each ejected droplet (including volume).FIGS. 13A-13B are used to discuss several options. Finally, in oneembodiment, a set of multiple, alternative droplet firing waveforms arecomputed in advance and made available for use with each print nozzle.This technique and related circuitry is discussed with reference toFIGS. 14A-C.

FIG. 12A provides a plan diagram 1201 of a print head 1203 traversing asubstrate 1205 in a scanning direction indicated by arrow 1207. Thesubstrate is seen here to consist of a number of pixels 1209 with eachpixel having wells 1209-R, 1209-G and 1209-B associated with respectivecolor components. Note again that this depiction is an example only,i.e., techniques as used herein can be applied to any layer of a display(e.g., not limited to individual color components, and not limited tocolor imparting layers); these techniques can also be used to makethings other than display devices. In this case, it is intended that theprint head deposit one ink at a time, and assuming that the inks arecolor component-specific, separate printing processes will be performed,each for one of the color components, for respective wells of thedisplay. Thus, if a first process is being used to deposit an inkspecific to red light generation, only a first well of each pixel, suchas well 1209-R of pixel 1209 and a similar well of pixel 1211, willreceive ink in the first printing process. In a second printing process,only the second well (1209-G) of pixel 1209 and a similar well of pixel1211 will receive a second ink, and so forth. The various wells are thusseen as three different overlapping arrays of target regions (in thiscase, fluid receptacles or wells).

The print head 1203 includes a number of nozzles, such as denoted usingnumbers 1213, 1215 and 1217. In this case, each of numbers refers to aseparate row of nozzles, with the rows extending along a column axis1218 of the substrate. Nozzles 1213, 1215 and 1217 are seen to form afirst column of nozzles, relative to the substrate 1205, and nozzles1229 represent a second column of nozzles. As depicted by FIG. 12A, thenozzles do not align with the pixels and, as the print head traversesthe substrate in a scan, some nozzles will pass over target regionswhile other nozzles will not. Furthermore, in the FIG., while printnozzles 1213, 1215 and 1217 precisely align to the center of a row ofpixels beginning with pixels 1209, while the print nozzles 1229 of thesecond column will also pass over the row of pixels beginning with pixel1211, the alignment is not precise to the center of the pixels. However,in many applications, the precise location at which the droplet isdeposited within a target region is not important, and suchmisalignments are acceptable. Note that this FIG. is illustrative only,e.g., in practice, the nozzles can be spaced closely enough in someembodiments that more than one nozzle of a single print head can be usedto deposit ink in a given well in any pass (e.g. as shown in thehypotheticals of FIGS. 1B and 3C.) The alignment/misalignment of thecolumns of nozzles with the rows of wells is respectively depicted bylines 1225 and 1227, which denote centers of print wells that are toreceive ink.

FIG. 12B provides a second view 1231, in which it is seen that all threerows of nozzles (or individual print heads) have been rotated byapproximately thirty degrees relative to axis 1218. This optionalcapability was referenced earlier by numeral 218 in FIG. 2A. Morespecifically, because of the rotation, the spacing of the nozzles alongthe column axis 1218 has now changed, with each column of nozzlesaligning with well centers 1225 and 1227. Note however, that because ofscanning motion 1207, nozzles from each column of nozzles will cross acolumn of pixels (e.g., 1209 and 1211) at different relative times, andthus potentially have different positional firing data (e.g., differenttiming for firing droplets). In some embodiments, such aspecifically-aligned arrangement is preferred, particularly in caseswhere it is necessary to precisely locate the deposited droplets withinthe target regions. In other embodiments, an arrangement in which thenozzles are not specially or precisely aligned to the target regions ispreferred, due to the reduced system complexity, particularly in caseswhere it is not necessary to locate each droplet in a precise locationwithin the target region.

As represented in FIG. 12C, in one embodiment, a print head optionallyendowed with multiple rows of nozzles can have such rows selectivelyoffset from one another. That is, FIG. 12C provides another plan view,where each of print heads (or nozzle rows) 1219, 1221 and 1223 areoffset relative to one another, as represented by offset arrows 1253 and1255. These arrows represent use of an optional motion mechanism, onefor each row of nozzles, to permit selective offset of the correspondingrow, relative to the print head assembly. This provides for differentcombinations of nozzles (and associated specific droplet volumes) witheach scan, and thus for different specific droplet combinations (e.g.,per numeral 1207). For example, in such an embodiment, and as depictedby FIG. 12C, such an offset permits both of nozzles 1213 and 1257 toalign with center line 1225 and thus have their respective dropletvolumes combined in a single pass. Note that this embodiment isconsidered a specific instance of embodiments which vary geometricsteps, e.g., even if the geometric step size between successive scans ofa print head assembly 1203 relative to the substrate 1205 is fixed, eachsuch scan motion of a given row of nozzles is effectively positioned ata variable offset or step using the motion mechanism relative to a givenrow's position in other scans. It should be appreciated, however, thatconsistent with the principles introduced earlier, such an embodimentpermits individual-per-nozzle droplet volumes to be aggregated inparticular combinations (or droplet sets) for each well, but with areduced number of scans or passes. For example, with the embodimentdepicted in 12C, three droplets could be deposited in each target region(e.g., wells for red color component) with each scan, and further, theoffsets permit planned variation of droplet volume combinations.

FIG. 12D illustrates a cross-section of a finished display for one well(e.g., well 1209-R from FIG. 12A), taken in the direction of scanning.In particular, this view shows the substrate 1252 of a flat paneldisplay, in particular, an OLED device. The depicted cross-section showsan active region 1253 and conductive terminals 1255 to receiveelectrical signals to control the display (including color of eachpixel). A small elliptical region 1261 of the view is seen magnified atthe right side of the FIG. to illustrate layers in the active regionabove the substrate 1252. These layers respectively include an anodelayer 1269, a hole injection layer (“HIL”) 1271, a hole transport layer(“HTL”) 1273, an emissive or light emitting layer (“EML”) 1275, anelectron transport layer (“ETL”) 1277 and a cathode layer 1278.Additional layers, such as polarizers, barrier layers, primers and othermaterials can also be included. In some cases, the OLED device caninclude only a subset of these layers. When the depicted stack iseventually operated following manufacture, current flow causes therecombination of electrons and “holes” in the EML, resulting in theemission of light. The anode layer 1269 can comprise one or moretransparent electrodes common to several color components and/or pixels;for example, the anode can be formed from indium tin oxide (ITO). Theanode layer 1269 can also be reflective or opaque, and other materialscan be used. The cathode layer 1278 typically consists of patternedelectrodes to provide selective control to each color component for eachpixel. The cathode layer can comprise a reflective metal layer, such asaluminum. The cathode layer can also comprise an opaque layer or atransparent layer, such as a thin layer of metal combined with a layerof ITO. Together, the cathode and anode serve to supply and collect theelectrons and holes that pass into and/or through the OLED stack. TheHIL 1271 typically functions to transport holes from the anode into theHTL. The HTL 1273 typically functions to transport holes from the HILinto the EML while also impeding the transport of electrons from the EMLinto the HTL. The ETL 1277 typically functions to transport electronsfrom the cathode into the EML while also impeding the transport ofelectrons from the EML into the ETL. Together these layers thereby serveto supply electrons and holes into the EML 1275 and confine thoseelectrons and holes in that layer, so that they can recombine togenerate light. Typically, the EML consists of separately-controlled,active materials for each of three primary colors, red, green and blue,for each pixel of the display, and as mentioned, is represented in thiscase by a red light producing material.

Layers in the active region can be degraded through exposure to oxygenand/or moisture. It is therefore desired to enhance OLED lifetime byencapsulating these layers, both on faces and sides (1262/1263) of thoselayers opposite the substrate, as well as lateral edges. The purpose ofencapsulation is to provide an oxygen and/or moisture resistant barrier.Such encapsulation can be formed, in whole or in part, via thedeposition of one or more thin film layers.

The techniques discussed herein can be used to deposit any of theselayers, as well as combinations of such layers. Thus, in onecontemplated application, the techniques discussed herein provide theink volume for the EML layer for each of the three primary colors. Inanother application, the techniques discussed herein are used to provideink volume for the HIL layer, and so on. In yet another application, thetechniques discussed herein are used to provide ink volume for one ormore OLED encapsulation layers. The printing techniques discussed hereincan be used to deposit organic or inorganic layers, as appropriate tothe process technology, and layers for other types of displays andnon-display devices.

FIG. 13A is used to introduce nozzle drive waveform adjustment and theuse of alternate nozzle drive waveforms to provide different ejecteddroplet volumes from each nozzle of a print head. A first waveform 1303is seen as a single pulse, consisting of a quiet interval 1305 (0Volts), a rising slope 1313 associated with a decision to fire a nozzleat time t₂, a voltage pulse or signal level 1307, and a falling slope1311 at time t₃. Effective pulse width, represented by numeral 1309, isof duration approximately equal to t₃-t₂, depending on differencesbetween the rising and falling slopes of the pulse. In one embodiment,any of these parameters (e.g., rising slope, voltage, falling slope,pulse duration) can be varied to potentially change droplet volumeejection characteristics for a given nozzle. A second waveform 1323 issimilar to the first waveform 1303, except it represents a largerdriving voltage 1325 relative to the signal level 1307 of the firstwaveform 1303. Because of a larger pulse voltage and finite rising slope1327, it takes longer to reach this higher voltage, and similarly, afalling slope 1329 typically lags relative to a similar slope 1311 fromthe first waveform. A third waveform 1333 is also similar to the firstwaveform 1303 except, in this case, a different rising slope 1335 and ora different falling slope 1337 can be used instead of slopes 1313 and1311 (e.g., through adjustment of nozzle impedances). The differentslopes can be made either steeper or shallower (in the depicted case,steeper). With a fourth waveform 1343, by contrast, the pulse is madelonger, for example using delay circuits (e.g., a voltage-controlleddelay line) to increase both time of pulse at a given signal level (asdenoted by numeral 1345) and to delay the falling edge of the pulse, asrepresented by numeral 1347. Finally, a fifth waveform 1353 representsthe use of multiple, discrete signal levels as also providing a means ofpulse shaping. For example, this waveform is seen to include time at thefirst-mentioned signal level 1307, but then a slope that rises to asecond signal level 1355, applied halfway between times t₃ and t₂.Because of the larger voltage, a trailing edge of this waveform 1357 isseen to lag behind falling edge 1311.

Any of these techniques can be used in combination with any of theembodiments discussed herein. For example, drive waveform adjustmenttechniques can optionally be used to vary droplet volumes within a smallrange after scan motion and nozzle firing has already been planned, tomitigate line effect. The design of the waveform variation in a mannersuch that the second tolerance conforms to specification facilitates thedeposition of high-quality layers with planned non-random or plannedrandom variation. For example, returning to the hypothetical introducedearlier where a television maker specifies fill volumes of 50.00 pL±0.50%, per-region fill volumes can be calculated within a first rangeof 50.00 pL ±0.25% (49.785 pL-50.125 pL), with non-random or randomtechniques applied to waveform variation where the variationstatistically contributes no more than ±0.025 pL volume variation perdroplet (given 5 droplets required to reach the aggregate fill volume).Clearly, many variations exist.

As noted above, in one embodiment, represented by the fifth waveform1353 from FIG. 13A, multiple signal levels can be used to shape a pulse.This technique is further discussed in reference to FIG. 13B.

That is, in one embodiment, waveforms can be predefined as a sequence ofdiscrete signal levels, e.g., defined by digital data, with a drivewaveform being generated by a digital-to-analog converter (DAC). Numeral1351 in FIG. 13B refers to a waveform 1353 having discrete signallevels, 1355, 1357, 1359, 1361, 1363, 1365 and 1367. In this embodiment,each nozzle driver includes circuitry that receives and stores up tosixteen different signal waveforms, with each waveform being defined aseries of up to sixteen signal levels, each expressed as a multi-bitvoltage and a duration. That is to say, in such an embodiment, pulsewidth can effectively be varied by defining different durations for oneor more signal levels, and drive voltage can be waveform-shaped in amanner chosen to provide subtle droplet size variation, e.g., withdroplet volumes gauged to provide specific volume gradations incrementssuch as in units of 0.10 pL. Thus, with such an embodiment, waveformshaping provides ability to tailor droplet volumes to be close to atarget droplet volume value; when combined with other specific dropletvolumes, such as using the techniques exemplified above, thesetechniques facilitate precise fill volumes per target region. Inaddition, however, these waveform shaping techniques also facilitate astrategy for reducing or eliminating line effect; for example, in oneoptional embodiment, droplets of specific volumes are combined, asdiscussed above, but the last droplet (or droplets) is selected in amanner that provides variation relative to the boundaries of the desiredtolerance range. In another embodiment, predetermined waveforms can beapplied with optional, further waveform shaping applied as appropriateto adjust volume. In yet another example, the use of nozzle drivewaveform alternatives provides a mechanism to plan volumes such that nofurther waveform shaping is necessary.

Typically, the effects of different drive waveforms and resultantdroplet volumes are measured in advance. For each nozzle, up to sixteendifferent drive waveforms are then stored in a per-nozzle, 1 ksynchronous random access memory (SRAM) for later, elective use inproviding discrete volume variations, as selected by software. With thedifferent drive waveforms on hand, each nozzle is then instructeddroplet-by-droplet as to which waveform to apply via the programming ofdata that effectuates the specific drive waveform.

FIG. 14A illustrates such an embodiment, generally designated by numeral1401. In particular, a processor 1403 is used to receive data definingintended fill volumes per target region. As represented by numeral 1405,this data can be a layout file or bitmap file that defines dropletvolumes per grid point or positional address. A series of piezoelectrictransducers 1407, 1408 and 1409 generate associated ejected dropletvolumes 1411, 1412 and 1413, that are respectively dependent on manyfactors, including nozzle drive waveform and print-head-to-print-headmanufacturing variations. During a calibration operation, each one of aset of variables is tested for its effects on droplet volume, includingnozzle-to-nozzle variation and the use of different drive waveforms,given the particular ink that will be used; if desired, this calibrationoperation can be made dynamic, for example, to respond to changes intemperature, nozzle clogging, or other parameters. This calibration isrepresented by a droplet measurement device 1415, which providesmeasured data to the processor 1403 for use in managing print planningand ensuing printing. In one embodiment, this measurement data iscalculated during an operation that takes literally minutes, e.g., nomore than thirty minutes and preferably much less (e.g., for thousandsof print head nozzles and potentially dozens of possible nozzle firingwaveforms). This data can be stored in memory 1417 for use in processingthe layout or bitmap data 1405 when it is received. In oneimplementation, processor 1403 is part of a computer that is remote fromthe actual printer, whereas in a second implementation, processor 1403is either integrated with a fabrication mechanism for products (e.g., asystem for fabricating displays) or with a printer.

To perform the firing of droplets, a set of one or more timing orsynchronization signals 1419 are received for use as references, andthese are passed through a clock tree 1421 for distribution to eachnozzle driver 1423, 1424 and 1425 to generate the drive waveform for theparticular nozzle (1427, 1428 and 1429, respectively). Each nozzledriver has one or more registers 1431, 1432 and 1433, respectively,which receive multi-bit programming data and timing information from theprocessor 1403. Each nozzle driver and its associated registers receiveone or more dedicated write enable signals (we_(n)) for purposes ofprogramming the registers 1431, 1432 and 1433, respectively. In oneembodiment, each of the registers comprises a fair amount of memory,including a 1 k SRAM to store multiple, predetermined waveforms, andprogrammable registers to select between those waveforms and otherwisecontrol waveform generation. The data and timing information from theprocessor is depicted as multi-bit information, and although thisinformation can be provided either via a serial or parallel bitconnection to each nozzle (as will be seen in FIG. 14B, discussed below,in one embodiment, this connection is serial as opposed to the parallelsignal representation seen in FIG. 14A).

For a given deposition, print head or ink, the processor chooses foreach nozzle a set of sixteen drive waveforms that can be electivelyapplied to generate a droplet; note that this number is arbitrary, e.g.,in one design, four waveforms could be used, while in another, fourthousand could be used. These waveforms are advantageously selected toprovide desired variation in output droplet volume for each nozzle,e.g., to cause each nozzle to have at least one waveform choice thatproduces a near-ideal droplet volume (e.g., 10.00 pL) and to provide arange of deliberate volume variation for each nozzle. In variousembodiments, the same set of sixteen drive waveforms are used for all ofthe nozzles, though in the depicted embodiment, sixteen, possibly-uniquewaveforms are each separate defined in advance for each nozzle, eachwaveform conferring respective droplet volume characteristics.

During printing, to control deposition of each droplet, data selectingone of the predefined waveforms is then programmed into each nozzle'srespective registers 1431, 1432 or 1433 on a nozzle-by-nozzle basis. Forexample, given a target volume of 10.00 pL, nozzle driver 1423 can beconfigured through writing of data into registers 1431 to set one ofsixteen waveforms corresponding to one of sixteen different dropletvolumes. The volume produced by each nozzle would have been measured bythe droplet measurement device 1415, with nozzle-by-nozzle (andwaveform-by-waveform) droplet volumes registered by the processor 1403and stored in memory in aid of producing desired target fills. Theprocessor can, by programming the register 1431, define whether or notit wants the specific nozzle driver 1423 to output a processor-selectedone of the sixteen waveforms. In addition, the processor can program theregister to have a per-nozzle delay or offset to the firing of thenozzle for a given scan line (e.g., to align each nozzle with a gridtraversed by the print head, to correct for error, and for otherpurposes); this offset is effectuated by counters which skew theparticular nozzle by a programmable number of timing pulses for eachscan. In one embodiment, a sync signal distributed to all nozzles occursat a defined interval of time (e.g., one microsecond) and in anotherembodiment, the sync signal is adjusted relative to printer motion andsubstrate geography, e.g., to fire every micron of incremental relativemotion between print head and substrate. The high speed clock (φ_(hs))is run thousands of times faster than the sync signal, e.g., at 100megahertz, 33 megahertz, etc.; in one embodiment, multiple differentclocks or other timing signals (e.g., strobe signals) can be used incombination. The processor also programs values defining a grid spacing;in one implementation, the grid spacing is common to the entire pool ofavailable nozzles, though this need not be the case for eachimplementation. For example, in some cases, a regular grid can bedefined where every nozzle is to fire “every five microns.” In onecontemplated embodiment, a memory is shared across all nozzles thatpermits the processor to pre-store a number of different grid spacings(e.g., 16), shared across all nozzles, such that the processor can (ondemand) select a new grid spacing which is then read out to all nozzles(e.g., to define an irregular grid). For example, in an implementationwhere nozzles are to fire for every color component well of an OLED(e.g. to deposit a non-color-specific layer), the three or moredifferent grid spacings can be continuously applied in round robinfashion by the processor. Clearly, many design alternatives arepossible. Note that the processor 1403 can also dynamically reprogramthe register of each nozzle during operation, i.e., the sync pulse isapplied as a trigger to launch any programmed waveform pulse set in itsregisters, and if new data is asynchronously received before the nextsync pulse, then the new data will be applied with the next sync pulse.The processor 1403 also controls initiation and speed of scanning (1435)in addition to setting parameters for the sync pulse generation (1436).In addition, the processor controls rotation of the print head (1437),for the various purposes described above. In this way, each nozzle canconcurrently (or simultaneously) fire using any one of sixteen differentwaveforms for each nozzle at any time (i.e., with any “next” syncpulse), and the selected firing waveform can be switched with any otherof the sixteen different waveforms dynamically, in between fires, duringa single scan.

FIG. 14B shows additional detail of the circuitry (1441) used in such anembodiment to generate output nozzle drive waveforms for each nozzle;the output waveform is represented as “nzzl-drv.wvfm” in FIG. 14B. Morespecifically, the circuitry 1441 receives inputs of the sync signal, asingle bit line carrying serial data (“data”), a dedicated write enablesignal (we) and the high speed clock (φ_(hs)). A register file 1443provides data for at least three registers, respectively conveying aninitial offset, a grid definition value and a drive waveform ID. Theinitial offset is a programmable value that adjusts each nozzle to alignwith the start of a grid, as mentioned. For example, givenimplementation variables such as multiple print heads, multiple rows ofnozzles, different print head rotations, nozzle firing velocity andpatterns and other factors, the initial offset can be used to align eachnozzle's droplet pattern with the start of the grid, to account fordelays and other factors. The grid definition value is a number thatrepresents the number of sync pulses “counted” before the programmedwaveform is triggered; in the case of an implementation that prints flatpanel displays (e.g., OLED panels), the target regions to be printed inpresumably have one or more regular spacings relative to the differentprint head nozzles, corresponding to a regular (constant spacing) orirregular (multiple spacing) grid. As mentioned earlier, in oneimplementation, the processor keeps its own sixteen-entry SRAM to defineup to sixteen different grid spacings that can be read out on demand tothe register circuitry for all nozzles. Thus, if the grid spacing valuewas set to two (e.g., every two microns), then each nozzle would befired at this interval. The drive waveform ID represents a selection ofone of the pre-stored drive waveforms for each nozzle, and can beprogrammed and stored in many manners, depending on embodiment. In oneembodiment, the drive waveform ID is a four bit selection value, andeach nozzle has its own, dedicated 1 k-byte SRAM to store up to sixteenpredetermined nozzle drive waveforms, stored as 16×16×4B entries.Briefly, each of sixteen entries for each waveform contains four bytesrepresenting a programmable signal level, with these four bytesrepresenting a two-byte resolution voltage level and a two-byteprogrammable duration, used to count a number of pulses of thehigh-speed clock. Each programmable waveform can thus consist of (zeroto one) discrete pulses to up to sixteen discrete pulses each ofprogrammable voltage and duration (e.g., of duration equal to 1-255pulses of a 33 megahertz clock).

Numerals 1445, 1446 and 1447 designate one embodiment of circuitry thatshows how a specified waveform can be generated. A first counter 1445receives the sync pulse, to initiate a countdown of the initial offset,triggered by start of a new line scan; the first counter 1445 countsdown in micron increments and, when zero is reached, a trigger signal isoutput from the first counter 1445 to a second counter 1446; thistrigger signal essentially starts the firing process for each nozzle foreach scan line. The second counter 1446 then implements a programmablegrid spacing in increments of microns. The first counter 1445 is resetin conjunction with a new scan line, whereas the second counter 1446 isreset using the next edge of the high-speed clock following its outputtrigger. The second counter 1446, when triggered, and activates awaveform circuit generator 1447 which generates the selected drivewaveform shape for the particular nozzle. As denoted by dashed lineboxes 1448-1450, seen beneath the generator circuit, this latter circuitis based on a high speed digital-to-analog converter 1448, a counter1449, and a high-voltage amplifier 1450, timed according to thehigh-speed clock (φ_(hs)). As the trigger from the second counter 1446is received, the waveform generator circuit retrieves the number pairs(signal level and duration) represented by the drive waveform ID valueand generates a given analog output voltage according to the signallevel value, with the counter 1449 effective to hold DAC output for aduration according to the counter. The pertinent output voltage level isthen applied to the high-voltage amplifier 1450 and is output as thenozzle-drive waveform. The next number pair is then latched out fromregisters 1443 to define the next signal level value/duration, and soforth.

The depicted circuitry provides an effective means of defining anydesired waveform according to data provided by the processor 1403. Asnoted, in one embodiment, the processor decides upon a set of waveformsin advance (e.g., 16 possible waveforms, per-nozzle) and it then writesdefinition for each of these selected waveforms into SRAM for eachnozzle's driver circuitry, with a “firing-time” decision of programmablewaveform then being effected by writing a four-bit drive waveform IDinto each nozzles registers.

FIG. 14C provides a flow chart 1451 that discusses methods of usingdifferent waveforms per nozzle and different configuration options. Asdenoted by 1453, a system (e.g., one or more processors acting underinstruction from suitable software) selects a set of predeterminednozzle drive waveforms. For each waveform and for each nozzle (1455),droplet volume is specifically measured, e.g., using a laser measurementdevice or CCD camera for example. These volumes are stored in memoryaccessible to the processor, such as memory 1457. Again, measuredparameters can vary depending on choice of ink and many other factors;therefore, calibration is performed depending on those factors andplanned deposition activities. For example, in one embodiment 1461,calibration can be performed at the factory that manufactures the printhead or printer, and this data can be preprogrammed into a sold device(e.g., a printer) or made available for download. Alternatively, forprinters that possess an optional droplet measurement device or system,these volume measurements can be performed at first use (1463), e.g.,upon initial device configuration. In still another embodiment, themeasurements are performed with each power cycle (1465), for example,each time the printer is turned “on” or is awakened from a low-powerstate or otherwise moved into a state in which it is ready for printing.As mentioned previously, for embodiments where ejected droplet volumesare affected by temperature or other dynamic factors, calibration can beperformed on an intermittent or periodic basis (1467), for example,after expiration of a defined time interval, when an error is detected,at the state of each new substrate operation (e.g. during substrateloading and/or loading), every day, or on some other basis. Othercalibration techniques and schedules can also be used (1469).

The calibration techniques can optionally be performed in an offlineprocess, or during a calibration mode, as represented by processseparation line 1470. As mentioned, in one embodiment, such a process iscompleted in less than thirty minutes, potentially for thousands ofprint nozzles and one or more associated nozzle firing waveforms. Duringan online operation (or during a printing mode), represented below thisprocess separation line 1470, the measured droplet volumes are used inselecting sets of droplets per target region, based on specific,measured droplet volumes, such that droplet volumes for each set sum toa specific aggregate volume within a defined tolerance range, per 1471.The volumes per region can be selected based on a layout file, bitmapdata, or some other representation, as represented by numeral 1472.Based on these droplet volumes and the permissible combinations ofdroplet volumes for each target region, a firing pattern and/or scanpath is selected, in effect representing a particular combination ofdroplets (i.e., one of the acceptable sets of combinations) for eachtarget region that will be used for the deposition process, asrepresented by numeral 1473. As part of this selection or planningprocess 1473, an optimization function 1474 can optionally be employed,for example, to reduce the number of scans or passes to fewer than theproduct of the average number of droplets per target region times thenumber of rows (or columns) of target regions (e.g., to less than whatwould be required for one row of nozzles, turned 90 degrees such thatall nozzles in the row could be used in each scan for each affectedtarget region, and depositing droplets in multiple passes for each rowof target region, proceeding one row at a time). For each scan, theprint head can be moved, and per-nozzle waveform data can be programmedinto the nozzle to effectuate droplet deposition instructions accordingto the bitmap or layout file; these functions are variously representedby numerals 1477, 1479 and 1481 in FIG. 14C. After each scan, theprocess is repeated for an ensuing scan, per numeral 1483.

Note once again that several different implementations have beendescribed above which are optional relative to one another. First, inone embodiment, drive waveform is not varied, but remains constant foreach nozzle. Droplet volume combinations are produced, as necessary, byusing a variable geometric step representing print head/substrate offsetto overlay different nozzles with different rows of target regions.Using measured per-nozzle droplet volumes, this process permitscombination of specific droplet volumes to achieve very specific fillvolumes (e.g., to 0.01 pL resolution) per target region. This processcan be planned such that multiple nozzles are used to deposit ink indifferent rows of target regions with each pass. In one embodiment, theprint solution is optimized to produce the fewest scans possible and thefastest printing time possible. Second, in another embodiment, differentdrive waveforms can be used for each nozzle, again, using specificallymeasured droplet volumes. The print process controls these waveformssuch that specific droplet volumes are aggregated in specificcombinations. Once again, using measured per-nozzle droplet volumes,this process permits combination of specific droplet volumes to achievevery specific fill volumes (e.g., to 0.01 pL resolution) per targetregion. This process can be planned such that multiple nozzles are usedto deposit ink in different rows of target regions with each pass. Inboth of these embodiments, a single row of nozzles can be used ormultiple rows of nozzles can used, arranged as one or more print heads;for example, in one contemplated implementation, thirty print heads canbe used, each print head having a single row of nozzles, with each rowhaving 256 nozzles. The print heads can be further organized intovarious different groupings; for example, these print heads can beorganized into groups of five print heads that are mechanically mountedtogether, and these resulting six groupings can be separately mountedinto a printing system at the same time so as to provide for concurrentfiring of nozzles from all of the print heads in a single scan. In yetanother embodiment, an aggregate print head having multiple rows ofnozzles that can further be positionally offset from each other, isused. This embodiment is similar to the first embodiment mentionedabove, in that different droplet volumes can be combined using variableeffective positional offsets or geometric steps. Once again, usingmeasured per-nozzle droplet volumes, this process permits combination ofspecific droplet volumes to achieve very specific fill volumes (e.g., to0.05 pL, or even to 0.01 pL resolution) per target region. This does notnecessarily imply that measurements are free from statisticaluncertainties, such as measurement error; in one embodiment, such erroris small and is factored into target region fill planning. For example,if droplet volume measurement error is ±a %, then fill volume variationacross target regions can be planned to within a tolerance range of atarget fill ±(b−an^(1/2))%, where ±(b²)% represents the specificationtolerance range and ±(n^(1/2)) represents the square root of the averagenumber of droplets per target region or well. Perhaps otherwise stated,a range that is smaller than specification can be planned for, such thatwhen expected measurement error is factored in, the resultant aggregatefill volumes for target region can be expected to fall within thespecification tolerance range. Naturally, the techniques describedherein can be optionally combined with other statistical processes.

Droplet deposition can optionally be planned such that multiple nozzlesare used to deposit ink in different rows of target regions with eachpass, with the print solution optionally being optimized to produce thefewest scans possible and the fastest printing time possible. Asmentioned earlier, any combination of these techniques with each otherand/or with other techniques can also be employed. For example, in onespecifically-contemplated scenario, variable geometric stepping is usedwith per-nozzle drive waveform variation and per-nozzle,per-drive-waveform volume measurements to achieve very specific volumecombinations, planned per target region. For example, in anotherspecifically-contemplated scenario, fixed geometric stepping is usedwith per-nozzle drive waveform variation and per-nozzle,per-drive-waveform volume measurements to achieve very specific volumecombinations, planned per target region.

By maximizing the number of nozzles that can be concurrently used duringeach scan and by planning droplet volume combinations such that theynecessarily meet specification, these embodiments promise high-qualitydisplays; by also reducing printing time, these embodiments help promoteultra-low per-unit printing costs, and thus lower the price point to endconsumers.

As also noted above, the use of precision fill volumes per target regionenables the use of advanced techniques that vary fill volumes accordingto defined criteria (within specification) so as to avoid line effect.This provides for further quality improvements relative to conventionalmethods.

The foregoing description and in the accompanying drawings, specificterminology and drawing symbols have been set forth to provide athorough understanding of the disclosed embodiments. In some instances,the terminology and symbols may imply specific details that are notrequired to practice those embodiments. The terms “exemplary” and“embodiment” are used to express an example, not a preference orrequirement.

As indicated, various modifications and changes may be made to theembodiments presented herein without departing from the broader spiritand scope of the disclosure. For example, features or aspects of any ofthe embodiments may be applied, at least where practical, in combinationwith any other of the embodiments or in place of counterpart features oraspects thereof. Thus, for example, not all features are shown in eachand every drawing and, for example, a feature or technique shown inaccordance with the embodiment of one drawing should be assumed to beoptionally employable as an element of, or in combination of, featuresof any other drawing or embodiment, even if not specifically called outin the specification. Accordingly, the specification and drawings are tobe regarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A method of manufacturing an electronic displayscreen having an array of pixels, the method employing a printheadhaving nozzles that eject droplets of a liquid onto a substrate, theliquid carrying a material that is to form a permanent layer of theelectronic display screen, the method comprising: for each nozzle of theprinthead, receiving an expected volume for a droplet of the liquidproduced by the nozzle in response to a nozzle drive waveform applied tothe nozzle, wherein the expected volume is dependent on empiricaldroplet measurement made for the nozzle and the nozzle drive waveformapplied to the nozzle relative to droplets of the liquid produced byother nozzles of the printhead; receiving data representing locations onthe substrate which are to receive the liquid, wherein each location isto receive a desired aggregate volume comprising multiple droplets ofthe liquid; for each location, calculating a combination of dropletsfrom one or more of the nozzles of the printhead where the correspondingexpected volumes sum to a value that necessarily lies within apredetermined range associated with the desired aggregate volume forthat location; and depositing the liquid onto to the substrate in eachlocation according to the respective combination, wherein depositingincludes causing relative motion between the printhead and the substrateaccording to scan paths that permit concurrent deposition of liquid inrespective ones of the locations according to the respectivecombinations.
 2. The method of claim 1, wherein calculating acombination includes: determining multiple combinations for each ofadjacent ones of the locations, each one of the multiple combinationsrepresenting droplets from one or more of the nozzles of the printheadwhere the corresponding expected volumes sum to a value that necessarilylies within a predetermined range associated with the desired aggregatevolume for that location; and for each of the adjacent ones of thelocations, selecting a specific one of the multiple combinations for thelocation, the selecting performed in a manner such that minimizes anumber of the scan paths needed to deposit the liquid according to thecombinations for the adjacent ones of the locations.
 3. The method ofclaim 1, wherein calculating a combination includes: determiningmultiple combinations for each of adjacent ones of the locations, eachone of the multiple combinations representing droplets from one or moreof the nozzles of the printhead where the corresponding expected volumessum to a value that necessarily lies within a predetermined rangeassociated with the desired aggregate volume for that location; and foreach of the adjacent ones of the locations, selecting a specific one ofthe multiple combinations for the location, the selecting performed in amanner such that minimizes time needed to deposit the liquid accordingto the combinations for the adjacent ones of the locations.
 4. Themethod of claim 1, wherein: causing relative motion according to scanpaths includes utilizing a sequence of geometric steps, each step in thesequence represents an incremental displacement of the printhead in adirection perpendicular to the scan paths, the sequence used to applythe liquid to a first portion of the substrate; and depositing includesrepeating the sequence to apply the liquid to a second portion of thesubstrate.
 5. The method of claim 1, wherein: the method furthercomprises, following the depositing, transporting the substrate to acure chamber, and curing the material to form the permanent layer of theelectronic display screen; and the depositing, transporting and curingare all performed in a controlled atmosphere that does not expose thesubstrate with deposited liquid to ambient air prior to the curing. 6.The method of claim 5, wherein the cure chamber includes a source ofultraviolet light, and wherein: curing includes exposing the substratewith the deposited liquid to ultraviolet light, to harden the materialinto the permanent layer.
 7. The method of claim 5, wherein theelectronic display screen is a first electronic display screen andwherein the substrate corresponds to panels, wherein each of the panelsto form a separate electronic display screen, and wherein one of thepanels corresponds to the first electronic display screen, and wherein:the depositing is performed as an integral print process that depositsthe liquid for all of the panels, and the curing is performed after thedepositing to harden the material carried by the liquid for each of thepanels; and the method further comprises, following the curing, cuttingthe substrate to separate the first electronic display panel from othersof the panels.
 8. A method of manufacturing an electronic display screenhaving an array of pixels, the method employing a printhead havingnozzles that eject droplets of a liquid onto a substrate, the liquidcarrying a material that is to form a permanent layer of the electronicdisplay screen, the method comprising: for each nozzle of the printhead,receiving an expected volume for a droplet of the liquid produced by thenozzle in response to a nozzle drive waveform applied to the nozzle,wherein the expected volume is dependent on empirical dropletmeasurement made for the nozzle and the nozzle drive waveform applied tothe nozzle relative to droplets of the liquid produced by other nozzlesof the printhead; wherein each nozzle in at least a subset of thenozzles is adapted to be driven by a selected one of predetermined,alternative nozzle drive waveforms, and wherein receiving an expectedvolume for each nozzle of the at least a subset includes receiving anexpected volumes for each respective one of the predetermined,alternative nozzle drive waveforms that can be selected for the nozzle;receiving data representing locations on the substrate which are toreceive the liquid, wherein each location is to receive a desiredaggregate volume comprising multiple droplets of the liquid; for eachlocation, calculating a combination of droplets from one or more of thenozzles of the printhead where the corresponding expected volumes sum toa value that necessarily lies within a predetermined range associatedwith the desired aggregate volume for that location; and depositing theliquid onto to the substrate in each location according to therespective combination; wherein depositing includes causing relativemotion between the printhead and the substrate according to scan pathsthat permit concurrent deposition of liquid in respective ones of thelocations according to the respective combinations, and whereindepositing includes, for each nozzle from the at least a subsetcorresponding to an expected volume represented by one of thecombinations, causing application to the nozzle of the one of thepredetermined, alternative nozzle drive waveforms which produced theexpected volume in order to produce a droplet of the liquid.
 9. Themethod of claim 8, wherein: the method further comprises deliberatelyvarying the value from location-to-location according to a randomizationfunction; and the predetermined range is common to all of the locations,such that the value from location-to-location according to therandomization function is to nevertheless necessarily fall within thepredetermined range common to all of the locations.
 10. The method ofclaim 8, wherein calculating a combination includes: determiningmultiple combinations for each of adjacent ones of the locations, eachone of the multiple combinations for the location representing dropletsfrom one or more of the nozzles of the printhead where the correspondingexpected volumes sum to a value that necessarily lies within apredetermined range associated with the desired aggregate volume forthat location; and for each of the adjacent ones of the locations,selecting a specific one of the multiple combinations, the selectingperformed in a manner such that minimizes a number of the scan pathsneeded to deposit the liquid according to the combinations for theadjacent ones of the locations.
 11. The method of claim 8, whereincalculating a combination includes: determining multiple combinationsfor each of adjacent ones of the locations, each one of the multiplecombinations for the location representing droplets from one or more ofthe nozzles of the printhead where the corresponding expected volumessum to a value that necessarily lies within a predetermined rangeassociated with the desired aggregate volume for that location; and foreach of the adjacent ones of the locations, selecting a specific one ofthe multiple combinations, the selecting performed in a manner such thatminimizes time needed to deposit the liquid according to thecombinations for the adjacent ones of the locations.
 12. The method ofclaim 8, wherein: causing relative motion according to scan pathsincludes utilizing a sequence of geometric steps, each step in thesequence represents an incremental displacement of the printhead in adirection perpendicular to the scan paths, the sequence used to applythe liquid to a first portion of the substrate; and depositing includesrepeating the sequence to apply the liquid to a second portion of thesubstrate.
 13. The method of claim 8, wherein: the method furthercomprises, following the depositing, transporting the substrate to acure chamber, and curing the material to form the permanent layer of theelectronic display screen; and the depositing, transporting and curingare all performed in a controlled atmosphere that does not expose thesubstrate with deposited liquid to ambient air prior to the curing. 14.The method of claim 13, wherein the cure chamber includes a source ofultraviolet light, and wherein: curing includes exposing the substratewith the deposited liquid to ultraviolet light, to harden the materialinto the permanent layer.
 15. The method of claim 13, wherein theelectronic display screen is a first electronic display screen andwherein the substrate corresponds to panels, wherein each of the panelsto form a separate electronic display screen, and wherein one of thepanels corresponds to the first electronic display screen, and wherein:the depositing is performed as an integral print process that depositsthe liquid for all of the panels, and the curing is performed after thedepositing to harden the material carried by the liquid for each of thepanels; and the method further comprises, following the curing, cuttingthe substrate to separate the first electronic display panel from othersof the panels.
 16. The method of claim 8, wherein: each of the nozzlesof the printhead is adapted to be driven by a selected one ofpredetermined, alternative nozzle drive waveforms; wherein receiving anexpected volume for each nozzle of the printhead includes receiving anexpected volume for each respective one of the predetermined,alternative nozzle drive waveforms that can be selected for the nozzle;and depositing includes, for each combination, causing application toeach nozzle in the combination of the one of the predetermined,alternative nozzle drive waveforms which produced the expected volumerepresented by the combination, in order to produce a droplet of theliquid.
 17. The method of claim 16, wherein: the method furthercomprises, separately, for each nozzle of the printhead, programing inadvance each of the predetermined alternate nozzle drive waveforms forthe nozzle into storage space respective to the nozzle.
 18. A method ofmanufacturing an organic light emitting diode (OLED) electronic displayscreen having an array of pixels, the method employing a printheadhaving nozzles that eject droplets of a liquid onto a substrate, theliquid carrying a material that is to form a permanent, light-generatinglayer of the OLED display screen, the method comprising: for each nozzleof the printhead, receiving an expected volume for a droplet of theliquid produced by the nozzle in response to a nozzle drive waveformapplied to the nozzle, wherein the expected volume is dependent onempirical droplet measurement made for the nozzle and the nozzle drivewaveform applied to the nozzle relative to droplets of the liquidproduced by other nozzles of the printhead; wherein each nozzle in atleast a subset of the nozzles is adapted to be driven by a selected oneof predetermined, alternative nozzle drive waveforms, and whereinreceiving an expected volume for each nozzle of the at least a subsetincludes receiving an expected volumes for each respective one of thepredetermined, alternative nozzle drive waveforms that can be selectedfor the nozzle; receiving data representing fluidic wells on thesubstrate which are to receive the liquid, wherein each fluidic well isto receive a desired aggregate volume comprising multiple droplets ofthe liquid and is to form a light generating element of a respective oneof the pixels; for each fluidic well, calculating a combination ofdroplets from one or more of the nozzles of the printhead where thecorresponding expected volumes sum to a value that necessarily lieswithin a predetermined range associated with the desired aggregatevolume for that fluidic well; and depositing the liquid onto to thesubstrate in each fluidic well according to the respective combination;wherein depositing includes causing relative motion between theprinthead and the substrate according to scan paths that permitconcurrent deposition of liquid in respective ones of the fluidic wellsaccording to the respective combinations, and wherein depositingincludes, for each nozzle from the at least a subset corresponding to anexpected volume represented by one of the combinations, causingapplication to the nozzle of the one of the predetermined, alternativenozzle drive waveforms which produced the expected volume in order toproduce a droplet of the liquid.
 19. The method of claim 18, whereincalculating a combination includes: determining multiple combinationsfor each of adjacent ones of the fluidic wells, each one of the multiplecombinations representing droplets from one or more of the nozzles ofthe printhead where the corresponding expected volumes sum to a valuethat necessarily lies within a predetermined range associated with thedesired aggregate volume for that fluidic well; and for each of theadjacent ones of the fluidic wells, selecting a specific one of themultiple combinations for the fluidic well, the selecting performed in amanner such that minimizes a number of the scan paths needed to depositthe liquid according to the combinations for the adjacent ones of thefluidic wells.
 20. The method of claim 19, wherein: the method furthercomprises deliberately varying the value from fluidic well-to-fluidicwell according to a randomization function; and the predetermined rangeis common to all of the fluidic wells, such that the value from fluidicwell-to-fluidic well varied according to the randomization function isto nevertheless necessarily fall within the predetermined range commonto all of the fluidic wells.
 21. The method of claim 19, wherein:causing relative motion according to scan paths includes utilizing asequence of geometric steps, each step in the sequence represents anincremental displacement of the printhead in a direction perpendicularto the scan paths, the sequence used to apply the liquid to a firstportion of the substrate; and depositing includes repeating the sequenceto apply the liquid to a second portion of the substrate.
 22. The methodof claim 19, wherein: the method further comprises, following thedepositing, transporting the substrate to a cure chamber, and curing thematerial to form the permanent, light-generating layer of the OLEDdisplay screen; and the depositing, transporting and curing are allperformed in a controlled atmosphere that does not expose the substratewith deposited liquid to ambient air prior to the curing.
 23. The methodof claim 18, wherein calculating a combination includes: determiningmultiple combinations for each of adjacent ones of the fluidic wells,each one of the multiple combinations representing droplets from one ormore of the nozzles of the printhead where the corresponding expectedvolumes sum to a value that necessarily lies within a predeterminedrange associated with the desired aggregate volume for that fluidicwell; and for each of the adjacent ones of the fluidic wells, selectinga specific one of the multiple combinations for the fluidic well, theselecting performed in a manner such that minimizes time needed todeposit the liquid according to the combinations for the adjacent onesof the fluidic wells.
 24. The method of claim 23, wherein: the methodfurther comprises deliberately varying the value from fluidicwell-to-fluidic well according to a randomization function; and thepredetermined range is common to all of the fluidic wells, such that thevalue from fluidic well-to-fluidic well varied according to therandomization function is to nevertheless necessarily fall within thepredetermined range common to all of the fluidic wells.
 25. The methodof claim 23, wherein: causing relative motion according to scan pathsincludes utilizing a sequence of geometric steps, each step in thesequence representing an incremental displacement of the printhead in adirection perpendicular to the scan paths, the sequence used to applythe liquid to a first portion of the substrate; and depositing includesrepeating the sequence to apply the liquid to a second portion of thesubstrate.
 26. The method of claim 23, wherein: the method furthercomprises, following the depositing, transporting the substrate to acure chamber, and curing the material to form the permanent,light-generating layer of the OLED display screen; and the depositing,transporting and curing are all performed in a controlled atmospherethat does not expose the substrate with deposited liquid to ambient airprior to the curing.
 27. The method of claim 18, wherein the OLEDdisplay screen is a first OLED display screen and wherein the substratecorresponds to panels, wherein each of the panels to form a separateOLED display screen, and wherein one of the panels corresponds to thefirst OLED display screen, and wherein: the depositing is performed asan integral print process that deposits the liquid for all of thepanels, and the curing is performed after the depositing to harden thematerial carried by the liquid for each of the panels; and the methodfurther comprises, following the curing, cutting the substrate toseparate the first OLED display panel from others of the panels.
 28. Themethod of claim 18, wherein: each of the nozzles of the printhead isadapted to be driven by a selected one of predetermined, alternativenozzle drive waveforms; wherein receiving an expected volume for eachnozzle of the printhead includes receiving an expected volume for eachrespective one of the predetermined, alternative nozzle drive waveformsthat can be selected for the nozzle; and depositing includes, for eachcombination, causing application to each nozzle in the combination ofthe one of the predetermined, alternative nozzle drive waveforms whichproduced the expected volume represented by the combination, in order toproduce a droplet of the liquid.
 29. The method of claim 28, wherein:the method further comprises, separately, for each nozzle of theprinthead, programming in advance each of the predetermined alternatenozzle drive waveforms for the nozzle into storage space respective tothe nozzle.